I agree that a vascular anomalies specialist is the way to go. I don't think it matters how many hemangiomas a child has...it just matters what is going on with them and what kind of treatments are suggested. I have heard before that if a child has multiple hemangiomas they may be at risk for internal ones...maybe that's the 3 or more guideline thing you were speaking of?? But I think seeing a vascular specialist is completely normal for having only 1 or 2 hemangiomas.
3 of my children have hemangiomas. They each only have 1 hemangioma. One required a specialist and had oral steroid treatment, surgery and laser. One saw a specialist but didn't have treatment and the other just has a teeny-tiny one on her arm.
I would definitely see a specialist where you have concerns about the size of her leg. Maybe it is not really a hemangioma? They are difficult to diagnose sometimes. I'm not sure where you live, but you could on the list here for doctor's names.
Good luck! Keep us posted!