My 10 week old has a hemangioma on her left arm, and is increasing in size. She was full term. Is there anything to stop it from getting larger?

Please see below. Hemangiomas are fairly common, occurring in up to 10% of full-term babies by 1 year old, especially females. Most of the time they don't cause any complications, so no treatment is needed. Initially they grow very quickly, but after 4-6 months, growth slows, then stops. They then start slowly shrinking; most resolve by age 9.
Propranolol. Not all hemangiomas need to be treated, but if it is growing rapidly, ulcerating, or causing other problems, it could be treated safely and effectively with oral propranolol. This is now the first line treatment of choice over steroids, surgery, or other modalities.
Not a hemangioma. If it is increasing in size in a 10 year old, it is not a hemangioma. It is some other type of vascular anomaly such as a venous malformation, or other possibilities. You should take her to a dermatologist or other vascular anomaly specialty center.
Early intervention. While most hemangiomas (fortunately) do not require treatment, those that occur within the head and neck area, or those that grow significantly and become raised should be evaluated by a vascular birthmark specialist. Early treatments include laser therapy, steroid therapy, and/or topical therapy. Each case should be evaluated individually, as no two hemangiomas are every quite the same.
Dr Juster's Answer. I agree , but if necessary there are treatments available from either a pediatric dermatologist or plastic surgeon.