[...Would she be offended if he just calls her Ardenbury in the future out of habit—]

...Miss Ardenbury, then.

[He'll try to remember, however, as he despite how he can be, he'll respect one's preference. For the most part, anyway.]

If you ever need assistance you can call me and I can see what I can do. I'm still training my skills, and I'm more proficient with dogs and other canines. But you don't need to worry about returning any favors.