You have probably already had this conversation, but I would ask my student “how will you feel if you get into school A and your process is over?” For one of my kids, they were thrilled with that notion and happy to be done. For the other, they would agonize over “what if” and “why didn’t I” for the remaining months of senior year.
I think it’s rationale and smart to get it done by going with choice A, provided you are pretty sure your kid won’t be having regrets all senior year or starting at the school with less than excitement.