S.D.
You're probably missing her sleep cues and putting her down too late. The first time she yawns or her eyes get droopy, put her down. If you wait until she's fussy, it's too late and it will mess with her sleep sequences. Put her down between 6:30 and 8:00 at the first chance you get.
Also, she's is technically sleeping through the night already, so say a big prayer that it keeps up. 5 hours is considered sleeping through the night!