She's probably going through a growth spurt or changes in her sleep cycle. Can you adjust her daily schedule and maybe cut down on one of her afternoon or evening naps so she'll be more tired at night? Maybe put her to bed a tad later than she goes down right now? Also is she eating any solids yet like cereal, perhaps? Sometimes when they're going through a growth spurt, they'll wake up hungry. Make sure she's just had a bottle and/or some cereal when you put her down.

Six months is also prime make-or-break self-soother time. That is, she's at the age where she's learning that when she wakes up on her own in the night, she can just play in her crib and babble and move around and be just fine even if no one comes running in response. Try seeing if she'll settle down on her own and go back to sleep. If you can get her to a point where she soothes herself and goes back to sleep on her own, the rest of her babyhood and toddler years are going to be a lot easier on her parents. If she's wide awake, throws a fit and the crying volume just continues to increase, you'll know you don't have a self-soother on your hands. At least not quite yet, that is. Good luck!!!