If this all just happened within the past day then just get her into be spayed right away and there shouldn't be any problems. I wouldn't even bother mentioning that your boy got on her. I also wouldn't worry about spay/abort because the babies aren't even in existance yet.
If you do have a problem with that, then just go in and say there is a chance she could be pregnant, but you aren't sure just please spay her and don't tell you if she was or not if it bothers you that much.
If you do have a problem with that, then just go in and say there is a chance she could be pregnant, but you aren't sure just please spay her and don't tell you if she was or not if it bothers you that much.