Welcome to HCM forum.
Yes for first timers taking hormonal
pills like thyroxine
( thyrocare) can cause some discomfort however it usually doesn't last more than a month.
The dose 25 mcg is a very minimal and safe dose.
If still your mother is having persistent discomfort I would advise you get her reevaluated by her doctor and get her hormone and calcium levels repeated for further management accordingly.
Hope I have answered your query.
Wishing you good health.