i was thinking general medicine, general surgery, or emergency medicine [when she performed cpr on the guy who was feeling uneasiness during vihaan's school event in the earlier episodes) but i havent seen a flashback whereby arambhi discussed about being interested in a specific specialty...i don't think she would be interested in dermatology/cosmetic surgery/plastic surgery given she's more about work rather than having flexible hours but i could be wrong and since avantika is already in that field..
I thought the CPR hinted towards cardiology but yeah it could be anything since all doctors are trained in general medicine & then comes the specialisation.
They could also establish her as a competitor for Avantika.

now whether she chooses to do cardiology or surgery only makers know lol...
