You mentioned that she had a public office job. If she is a politician, support to a politician, or even a key policy maker, that job comes with significant demands that they respond to constituents (if they ever want to be re-elected). This makes politicians notorious people-pleasers who are unable to say "no." For instance, if a meeting is scheduled from 1 PM to 2 PM they will attend, and spend another (unscheduled) hour or two talking with the public. Somebody calls at 4PM on a Sunday and wants support for a matter, well you can't just hang up on them.
She still is at fault for not realizing that her obligations have changed. Maybe her promises to spend time with you are another version of not being able to say no, or she wishes that she could hang out like the old days, but it's not the same anymore.
That doesn't mean that you have to keep including an unreliable person. I wouldn't, especially if it becomes costly. Your DH was justified in demanding the deposit money back.