One thing that's not clear in your post - Did you tell her point blank (or remind her point blank, in case she already knew but may have forgotten) that you are "deathly allergic" to cats? If you assumed that she was conscious of that when in fact she wasn't, I can see her side of the story. However, if you're 100% sure that she knew of the seriousness of your cat allergy at the time you were having that argument about the cat, then PLEASE don't get someone like that pregnant and be miserable for years to come.