I too use a locally bought Jamila henna. I don't henna for color though...never have. I use it solely for its strengthening and conditioning properties.
I cornrow my hair using the deep moisture method and wear them under wigs or turbans for 4 weeks at a time. I do everything in those braids - weekly DCs, weekly light or medium PTs, daily moisturizing and sealing, and co-washing 3x per week. I also apply MT to my scalp every other night.
When I take my braids down after the 4 weeks, I pre-poo overnight, detangle, clarify, and DC. I typically wear my hair out for 7-10 days after take-down.
When I'm ready to put the cornrows back in, I henna overnight, rinse thoroughly, then let the DC sit on my hair for a few hours before I cornrow it.
Hope this helps ma!