Have you tried a pacifier or soother? Some babies just have a strong urge to suck, and because she is not awake or rooting around, or crying, perhaps she is not hungry but just wants to be soothed? My son is the same way. If I didn't have a do other for him as he falls asleep he would never stop feeding
Soother* not do other lol.
Just let her eat and nurse as much as she wants. We get hungry in our sleep but we've learned to ignore it. She hasnt. I found its better if they don't wake up fully to nighttime nurse. It makes it easier for both of you to go back to sleep. It's normal. And time frame wise... every baby is different.