It doesn't sound great at all. What a disappointment. Especially considering you are at your most vulnerable when just returning from leave.
And, yes, most PR-type messages, and media seem to portray a much more positive attitude to part-time working, working mothers and returning to work after maternity leave. And indeed, compared to 10 or 25 years ago, it has become better and easier. Government figures even claim that over 70% (or perhaps it was even 90%) of requests for part-time work get accepted. In general the NHS (and educational sector) tend to be much better for part-time workers, however, as in any organisation, it seems to depend a lot on your individual manager.
However, I am afraid the reality for individual women is different. I meet so many women who struggled going part-time, or just didn't even try and I myself also didn't have a positive experience. Which is of course one of the reasons I am now running the website.
May I ask though, has your wife followed the appropriate, formal procedures for requesting flexible work, and have her requests and her employers responses properly documented?
All the very best, and do keep on supporting your wife.