Hi and welcome!
My best advice is for you to call her physician and schedule an appointment. The only time I've ever heard of rebound growth is when a child was on propanalol and, when the medicine was discontinued, the lesion grew again.
What treatments has your child had?
Please, take some photographs now for comparison.
You can ask one of our experts here: http://birthmark.org/experts.php
and be sure to include a photo and detailed explanations of any treatments to date. Also, has she had any other difficulties lately? It may even be related to some over-the-counter medication or new food, so any changes in the last two months? Children that age... it's difficult to pinpoint anything new, since, to them, everything is new!
Let us know what happens!!