Sounds like she is transitioning into retirement. My husband could probably technically take a week off a month. He's been working with his company for so long he accrues a huge amount of vacation time very quickly.

You could probably arrange your appointments, spacing-wise, so that you can still have 4 sessions a month (wouldn't be on the same day each week though), and the longest space between appointments in a month would be around 10 days which isn't too bad. Take a look at it and see what can be worked out. I know this is upsetting, but it might be workable. It does sound a bit like she's working toward retirement though, so you probably need to have that discussion with her.