I wouldn't have her go over 50mcg/day, and it would probably be a good idea to just go up to 25mcg/day.
Either way, I would slowly ramp the T3 up over 2 weeks:
6.25mcg - 4 days
12.5mcg - 4 days
18.75mcg - 4 days
25mcg - however long
And ramp down *slowly*:
18.75mcg - 8 days
12.5mcg - 8 days
6.25mcg - 8 days
Make sure she keeps an eye on her pulse, as rapid pulse rate is the bad side effect to watch out for.
All that being said, why doesn't she just get a referral to an endocronogist, get her thyroid levels checked and maybe get some meds prescribed???