I would try going back down to the smaller teat, I recently changed them for my lo and I thought she was ok as wasn’t spluttering everywhere ect but she just randomly stopped drinking as much, I thought it was due to me weaning her and wanting more food. We ended up going back down and she’s back to drinking more milk I think she just found it too fast so then just refused the bottle. So I would definitely give it a go going back down just to rule it out. X
Sounds like she’s getting the milk too fast, it’ll cause gas and discomfort, so she won’t want to feed. Just size the teat down again.
Maybe go back down a size of teat it might have been too soon for her?