There is a growth spurt at 6 months so she may be hungry. I think my LO is close in age to yours and although she hasn't been STTN as long as your LO, she's started waking at night for a feed again in the last few days. Like your LO, she doesn't really cry - she just lays there and moans and then I feed her, lay her down awake and she goes right back to sleep.