True, not all babies sleep 12 hours per night. If you are okay with her waking up at 5:15 AM, then you can shift the timeframe to accomodate that. Otherwise, treat it as a night waking and don't take her out of her crib. Maybe you can set your clock a little bit earlier so that you are essentially giving her a df (say at 4:30 AM) so that she will wake up later than 5:15 AM.
If she sleeps 10 hours per night, she may have to make up the hours somehow during the day, possibly an extended nap instead of a catnap in the afternoon. Keep in mind that babies need about 15-17 hours of sleep per day.
HTH