The only thing that was unique during Charles and Diana's sitution was the modern age press that made everything seem like it was the worst thing ever. Diana didn't do anything to threaten the monarchy.
Her relationship with the family was cool, but pretty much typical of a in-law relationship. We like each other today, but tomorrow can be another story.
She did, she talked about her marriage, she talked about the RF, she criticised the future King and gave her opinion that he didn't really want the "top job" and would not be that good in it. She did a secret interview, which was broadcast on TV.. without the queen's permission. That horrified her own staff who were trying to keep up a relationship with the RF and the queen..
That's about as bad as you can get, from a senior member of the family. She angered the queen during the divorce negotiations by putting out her own statement about her title before it had been agreed with the queen, and the queen was forced to put out a counter statement.
It was indeed not untypical of an "in laws" relationship, In that the young wife is never quite accepted by her husbands family.. and if there's a divorce, she's going to be disliked by the husband's family and seen as an interloper who caused problems. Only in this case the in law rows had constitutional implications.
Its not the same as many in law situations where a family never like the new bride.. at first the RF were quite prepared to accept Diana, liked her and were pleased she was in the family. but when they got her in, she never quite fit and was on uneasy tems with many of them from very early on.
I think one aspect of the situation that hasn't maybe been touched on is that the queen TRIED to overlook Di's faults for the sake of her good points. That she saw how popular and magnetic Diana was, and tried to be there to support her, even when she was getting uneasy and others in the RF were getting more critical. She seems to have been willing to listen to Diana, crying and complaining, even if she couldn't offer any constructive help
and I think she felt that she had to do this and keep Diana as calm as possible, because she was such an asset to the RF. But eventually I think she ran out of patience, and that's why she grew quite cool to her daughter in law, because she felt she had done her best, had put up with a lot and Diana still was not "settling" in the family....and had grown more alienated from them as time went on