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Dayjoy, I was panicking reading this and can't get to the end of it because I'm about to hyperventilate with impatience as I am itching to jump in.
Here's one thing you need to know about 4B hair or 4C whatever! You cannot take shrunken hair comb or brush (<---froths at the mouth at the thought of a brush through the hair. Nonie no likey brushes
) and then leave it loose and expect it to stay that way. It has to be "trained" albeit temporarily. If the hair isn't well moisturized (on the inside), then any moisture from the air will be absorbed into the hair and shrinkage will happen even faster.
Here's what I suggest (and you can take this up from whatever stage you are at now): When you wash her hair, make sure you first comb through a small section and braid that section. Comb through another section and braid it. When you have about 3 small sections undo them and then braid them together to ensure they stay detangled. (The reason for this is if you work on a large section, it'll overwhelm you. And if you work on small sections and don't braid them, they will shrink up. You end up undoing those small sections to create the sort of braid you would normally create if the hair wasn't quick to shrink.)** You must do that to all her hair so that by the time you're ready to wash they are all detangled and locked in braids so they cannot shrink up. And when you braid, braid to the ends or as close to them as possible so you stretch them out too.
Wet the hair while in braids and apply shampoo to each braids. Please use a moisturizing shampoo. At the risk of being stoned, I will tell you not to use CON. Please use any of the Giovanni moisturizing shampoos or Nexxus Therappe. The idea is a shampoo that is going to be adding moisture as well as making hair slippery. Squeeze each braid to get shampoo inside it, then use a wide comb to carefully undo the one braid. Stretch out the hair with one hand as you run the comb through with the other. Go to a smaller comb if you are able to. You may even find you can comb through with a fine-tooth comb. But if you can get a comb with teeth as wide as that metal pick with a fist, you're doing good.
This is how I suggest you comb. (Notice how I stretch the hair first so the comb has an open path).
Plait that section after combing through so it stays that way. And do the same to all the others. Notice what I am saying: you do not give the hair a chance to shrink back on itself.
When it's time to rinse, as the shower head sprays the head, (get one of those attachment that has a hose so that you DD can hold it toward your head and free you to work on her hair. Undo one plait, and as the water runs through it, use the help of the water stretching the hair to make the comb go through easily. In other words you first spray the whole head, then focus on one braid and let all the water run though it. Undo it to ensure you rinse properly and as water runs through it, comb through. You'll find that the water stretches out the hair but you can also use your hand. Then w/ water still running through the hair, braid it up and focus on rinsing another braid. Once all are rinsed, they should still be locked in braids fully detangled. Now comes the fun part: conditioning.
Apply a moisturizing conditioner to each braid, then undo one at a time and add more conditioner if needed and then comb through. Now you don't want to add too much till it's like glue. If it starts to feel that way, you need to wet it. You want the conditioner to make the hair feel slimy/slippery/smooth. I call this the fun part coz if you're going to enjoy combing the hair in the method I showed above, it is at the stage. The vid you saw above was conditioner in my hair. Once again, you will braid that up and then move on to another braid and smother it in conditioner and braid it up. If you have time to DC with heat, this would be a good time to do so...otherwise just leaving the conditioner on for a good spell is OK.
You will rinse like you did the shampoo and again braid it up. Then comes the most important part, IMO. The ACV rinse. I suggest getting a basin and filling it with water then adding 1/4 cup or 4 tablespoons of ACV. When I'm washing my hair, I just kneel in the tub and bend forward dunking my head in the solution. I then undo a braid and comb it while submerged in the solution to make sure all my strands are bathed nicely in it. Then I braid it back and do the same to another. If it's easier you can mix a very dilute solution of ACV in a bottle and then towel dry her braids after rinsing off the conditioner, and then re-wet each braid with the ACV spray. This way you know you are coating the strands with cuticle closing acidity. You can undo to make sure each is coated, then be very gentle stretching it to run the comb through it and rebraid it...making sure to braid as close to the tips of the hair as possible. The towel dry the braids and let them airdry fully w/o undoing.
When you undo them, you can use comb to start the undoing the point at the end of the braid, then use fingers, the hair should be stretched but still feel rough. I hope others will chime in on what "moisturizer" works well to keep hair feeling soft w/o shrinkage. I'm an S Curl whore so I don't mind shrinkage but I always feel as if coconut oil would be ideal for making hair feel moisturized w/o shrinkage. (I apologize for not knowing great moisturizers, but if there's one you like, then this is where to use it.) You will undo a braid and part a very narrow section and apply the moisturizer from base to ends as if it were relaxer. You will comb through and then do the same to the next. Remember, the goal is always not to let the hair shrink and if it were fully dry, you should see it behaving better by not shrinking up too much. If you can cornrow the hair after applying moisturizer, you will find the ends will be stretched out ever better. Or, if you find that when you braid single plaits you just can't get that tail end stretched, then you may need to thread the end: ask your daughter to hold the length of the braid so you're not pulling at her scalp, and you stretch the tip as you wrap it in thread completely. You'll be surprised at how smooth and straight those ends will look/feel.
Your post broke my heart because 4B hair is so easy to handle once you just get it. I wish you were not so far away, I'd love to do your daughter's hair.
Now you make me want to figure out what "moisturizer" doesn't cause shrinkage but moisturizes as well as S Curl. BTW, if shrinkage isn't a problem, then I recommend S Curl and can direct you to a post where I shared how to use it.
I'm sorry if this post was late...but I haven't had a chance to get on till now. Here's a big hug.
ETA** I decided to come back to this post to show you that even after wearing braid extensions for over a year and my hair is this stretched:
FF to 1:14 to get a glimpse of how stretched my hair is after being in braids, as I would undo a few braids, I would put them in bigger plaits as seen below:
Actually at the top corner of the top pic, you can see the base of a microbraid, but I didn't wait to undo all the braids and deal with tangles. I was making sure I braid them up ASAP to keep m hair stretched.
And like your DD, shrinkage doesn't take long to creep in if I leave the hair out. Below is that bottom braid undone...and you can see the hair is curling back on itself.
I don't use products when I wear braids so the dry hair doesn't have some form of coating to keep moisture out. But because I know this, I do not ever just leave my hair out unless I've taken precautions to make sure it'll not be a nightmare to deal with.
oke: 
I will plan a day for us and have my trusted stylist give me pointers too.
