Refusing to BF before bed

My almost 8-month old is almost EBF (nursing in the AM and before bed, bottled breast milk during the day) but recently she's been pretty much refusing to nurse before bed. She will nurse for a minute or two and then she'll bite down and pull back several times (and even without teeth, this kills!) and refuses to eat. However, if I give her a bottle of formula she will usually take it-- even up to 8 oz.-- so I know it's not that she's not hungry. What's going on?!