What's the rest of her regimen? Does she leave the relaxer on until it burns? Is she overlapping or running the relaxer through all of her hair, not just the new growth? Does she heat straighten (press/flat iron) often?
Personally, I think relaxer use over decades couldn't be healthy for anyone's scalp so she may want to start stretching for a long time (12+ weeks) or consider transitioning.
It may be a good idea for her to see a dermatologist to rule out female pattern baldness and other medical reasons for hair loss. She should also check and see if any medicines she's taking could be causing the hair loss (for example, steroids can cause hair loss like you wouldn't believe).
If there is no medical cause of her thinning hair then you'll have to see if she'll change her hair care. That means treating her hair gently, deep conditioning, moisturizing, protective styles, low/no heat, and less frequent relaxing. She could also look into using topical growth aids, like a sage/rosemary spritz, emu oil, tea/coffee rinsing, etc. If after 6 months of consistent care she doesn't see a difference then I'd be more likely to blame it on age. At this point, it's probably just bad hair care.
Welcome and I hope this helps!