Seems like I'm in the minority here, but I enjoyed Rose's backstory and did find it believable.
Clearly the writers wanted us to think that she was from Rhode Island, hence, the multiple mentions of Rose hating "Providence" rather than just saying she hated Oklahoma (assuming that most people would think of Rhode Island when they hear "Providence", which makes a lot of sense: old money, close to NYC, etc.) only to trick up with Providence, OK. As someone from New England, when we saw Rose in the car riding to Providence, I kept thinking that there was no way that 95N was that underdeveloped in the early 60s, so when "Providence, OK" appeared on screen, I chuckled at my own assumption.
However, once there....it made a lot of sense. She was treated like a child who only enjoyed baubles and clothes and had no other value, which explains her innate desire for a pampered lifestyle. But the last few seasons, we've seen the impact that Midge has had on her mother. Although, Rose doesn't want to admit it, I believe there is a lot of her that admires Midge's unconventional lifestyle. Although, she sticks to her cultural upbringing (i.e. pushing Midge to return to Joel, then pushing her to marry Benjamin, because what is a woman without a man?), I think there is a lot of change on the horizon for Rose She is growing more sure of herself, seeing more value in herself (hence, her Parisian expedition) and it will be a slow journey, but it is happening. After living her NY lifestyle for so long, being upfront with her husband, taking charge of her own life in Paris, and then returning to her childhood home as a woman/mother/grandmother, I definitely see how the demeaning attitude of her family and their attempt to reduce her to a child caused a switch to flip in her (and it was implied she doesn't see her family often, so this explains why her most recent visit affected her so much).
I'm sure she will definitely have some regrets about this choice, but I did find the manner in which she told her family off to be believable.