Are they regularly giving her a paci? I agree with the "switching bottle nipples" but also they should be regularly giving her a pacifier to help work out those muscles.
"Happy to starve" is a common problem with preemies as well, which it sounds like might be the issue. Feeding the baby is just going to be a major chore of encouraging those muslces. A spoon, straw, sippy cup etc. are all good options too.
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