Is she deliberately trying to sabotage your attempts to hide your old name? This would be a deal breaker for me - having a partner who does not respect my wishes. Maybe stop bringing her to parties and social events until she sorts out her habits. I have a name that I absolutely hate, my partner knows it and does not use it. He uses a shorter tolerable variation of it. There are also certain words that I absolutely cannot stand - "MAD". Fucking hate that word. had to just say it once to my partner and he got it.

From what you mentioned, it does not seem like it's slipping from her, rather she just does not want to use the new name.