Unfortunately, as hard as it is, if she breaks up with you over this without talking it out first, she's not worth keeping around.
If she won't accept this intimate part of you now, there's a good chance she wouldn't later either.
No matter what, remember that you're not hurting anyone nor yourself with ABDL and it's a very good healthy way to destress. Sure it may seem taboo to people outside our circle, but it's valid nonetheless.