Hi sis, I went through something similar also around this age, so I know how worrying it feels when they suddenly reject milk and food. At 17 months, appetite can fluctuate a lot, and sometimes they are just going through a phase or getting more independent, not necessarily something wrong with them. If she is still active and having wet diapers, I would try not to force the milk and instead offer smaller amounts more frequently and focus more on solids first. You can also check with your PD if she needs that much formula at this age or if it is okay to slowly reduce, just to ease your mind.