Levothyroxine dosage

Hi there my youngest daughter who is 27 is having problems getting the correct dosage for her bodies needs. She was started on a low dosage of 25 mcgs earlier this year after we managed to get her retested for under active thyroid plus tpoab antibodies, which were slightly elevated and the usual vit D, B12, ferritin and folate which were all low In range. Under active thyroid runs in my family, my mother dying from undiagnosed hypothyroidism 16 years ago. Myself and my oldest daughter are both hypo as well but seem to have got on ok ish with levothyroxine, my dose being started off at 100 mcgs never altered until I started the menopause lowering to 75mcgs ? Going back to my youngest daughters problem, after 2 months of being on 25mcgs the dose was increased to 50 mcgs ! this was too much sending her over medicated in July 2016 her serum free T4 result was 35pmo/L (ref range 9-23pmoL and her serum tsh level was 0.02mu/L (ref range 0.55-4.8mu/L). she was having palpitations and felt anxious, couldn't sleep and sweating, her blood pressure was also very high. The doctor suggested lowering the dose to 50mcg every other day,rightly or wrongly I suggested 25mcg every day so splitting the tablet ? A month later August it was retested tsh was 0.01 mu/L (range0.55-4.8 mu/L) and Free t4 had dropped to 24 pmo/L (range 9-23 pmo/L) so carried on with dosage 25 mcg daily, she has been to Australia for a month in the meantime and taken 3 lots of antibiotics in that time. Having her bloods retested this week October her free t4 has dropped down to 12 pmo/L (9-23) and her tsh has elevated to 5 mu/L the highest it has ever been before and since starting medication. So I am suggesting she alternate 50 /25 mcg ? So Does taking levothyroxine stop the thyroid from working all together ? And does anyone know if the antibiotics she took would affect the stomachs absorption of Levothyroxine. She has chosen to take her levothyroxine before bed ! I know it's fine tuning and trial and error I have suggested she gets Vit D ferritin, b12, folate retested next time bloods are checked, as I know how important vits and minerals are in supporting the thyroid function. Also as these tests were low in range originally do you think we jumped in too quickly with accepting the thyroid medication and should have looked at gut absorption issues first ? Her serum folate in may was 6.9 ug/L > 3.4ug/L , B12 had increased to 401ng\L supplementing with sublingual spray, Last test for Vit D was October 2015 with a total of 59 nmo/L was advised by Gps to carry on supplementing as winter months . Ferritin was last tested Nov 2015 where it had dropped to 51 ug/L from 61ug/L in April 2015 range 20- 291ug/L her immune system seemed shot.

Appreciate any advice

Many thanks

Fae1960