Dilemma please help

So I’m a nanny to 3 kids aged 5, 2 & 3 months old. The baby is nursed by mom and she leaves 3 pre-made pumped bottles in the fridge for the day. Usually the baby takes them totally fine and is a really good eater. Yesterday I noticed that she was drinking an ounce and then screaming bloody murder and refusing the rest of the bottle. She was choking on the milk and spitting up like crazy. I finally checked her nipple size and they changed it to a size 3! (Usually for very old babies. Babies 6 months and under should use size 1!). All of the bottles had this nipple size. At the end of the day I mentioned that she was struggling with her bottles and the mom said “oh well we just switched her to faster flow nipples” like it was no big deal. I really don’t want to step on her toes or feel like I’m telling her what to do because she is very possessive over the baby and already is struggling to not be the one with her every day. She’s not a first time mom and she’s also a nurse practitioner so I feel like common sense would say that the nipples are way to big. What should I do or say to avoid sounding like I’m stepping on her toes. Please help