We may need to know more about your mom's hair. All gray hair isn't the same. Some have wiry hair. Some have soft hair. Some of it will straighten out. Some of it will curl.
You are going to have to do some detective work with her hair.
1. What is the density? Low, medium, high --- low density, trying to combat alopecia, hormonal issues and meds that thin your hair.
2. Are her strands fine, normal, coarse ------ fine
3. What's her porosity: low, normal, high ----- high porosity
4. Does she have small curls, bigger curls, kinks, coils? No curls. Soft wave
How does she care for it now?