Warts are caused by a virus and this child seems to have an active virus living on his hands and it can be easily transmitted to other parts of his body. It's too bad that school is already out, as may be the school nurse could have sent a note home explaining how they spread, having that impartial party speak with her would have been less confrontational. It's important for the boy to have this problem cared for. I would try again or get some information on treatment and give it to her. Maybe the reason she doesn't want to get care is because of the 'several' visit prospect... it's a copay for each visit and maybe their family finances won't support this regime. Compound W now has a quick freeze product that may do the trick. Whatever the family is capable or willing to do, you'll have to live with. Don't draw attention to the warts in front of the young man or discuss his condition with anyone in his presence. Under no circumstances do you talk with your kids about his warts.
Some warts will eventually fall off, after a few years, others don't. It takes a pediatrician, primary care doc or a dermatologist to make that determination. Again, offer her information from your pediatrician's office, from the net (WebMD or something similar). It's great that you're a concerned friend, but somethings are beyond our control and their's, especially when finances are concerned and this isn't a health hazard.