Bj - say to yourself - three month growth spurt. I bet thats what it is, or else it has thrown her off-track and then left her with the bad habit when it left. Is she still feeding more and frequently? How many oz is she taking and how often? Have you increased this recently? Is she swaddled, in a grobag or equivalent, is it too hot or cold, does she wake at the same time exactly each night or is it random? If it is random, she maybe hungrty so you might try putting her on 2.5 hourly feeds during the day, or adding a cluster feed etc. If it is the same time everyday, it may be a habitual waking and you may need to break this habit.
Hugs to you my love x x