J.W.
A six month old doesn't physically need to wake up and eat in the middle of the night, so I would say she's doing it out of habit. At her last feeding before bedtime, I would give her a little extra to eat, and when she started crying, I'd just put a pillow over my head and watch the clock. Try to ignore her for a few minutes and then go over and lay her back down. I can't say it won't be rough for a few nights, but it will work if you stick with it. Children quit physically needing to eat that nighttime feeding by about 6-8 weeks old. Hope it helps.
J. W.