Hi and welcome!
The term "vascular malformation" covers a broad spectrum of birthmarks, including hemangioma and port wine stain. Venous malformation is more specific and refers to a mass of blood vessels.
I don't know how much OTC pain reliever is too much, but if you're asking, then she probably needs some pain management. How old is your daughter?
I know there are others here who take other medications for pain. However, that decision is affected by a wealth of things, including age and activity level. This is something that needs to be discussed with her doctor.
If you will let us know where you are located, then we can help you find a physician that deals with these lesions specifically. Because you are not in the "hemangioma" forum, I suspect that your daughter is older and that you've gotten a good diagnosis (these are often misdiagnosed or misnamed), but if we can help you get other opinions, let us know!