Wow this has been a fascinating thread.
You sound exactly like the ex GF of my DH's brother. My MIL wanted us to have a family gathering as a memory to DH's dad who had sadly died the year before. She booked us all rooms in a lovely hotel up where DBIL was going to be playing in a band. She sent the information round to DH and myself, her sister, DH's brother and his then GF (who you OP are reminding me of).
Ex GF kicked off saying she'd been brought up to always pay her way independently and not take anyone's money. MIL said fine I understand that but hotel room is paid, I've done it for everyone including my sister and her DH we are going to support DS (my DBIL's) band and in memory of my DFIL. So it's my treat (so says my MIL). DH and I and rest of family accepted this, thanked her profusely and said we would pay for the meal when we got there which she then accepted.
The point was she made the plans and she wanted us all there in memory of her DH and that's why she was generously paying the hotel rooms.
Ex GF of DBIL sent a terse angry message saying she would prefer to pay her own way or she won't go. MIL got v upset as she saw it as a rejection of her goodwill and DBIL was v stressed being caught between his mum and then GF.
In the end she didn't go and she must have bitched to HER DM about it as next time DMIL went out with her, her son and Ex GF's DM the DM got v drunk and started swearing and shouting at DMIL telling her she insulted her DD by paying for the hotel.
They were such an obtuse family. The ex GF was the worst though. One time when they turned up at our house I made a joke that she was only here to see my pets (the one thing she softened to) and she got extremely huffy with me and said how dare I suggest that; she was there to see me and DH. Took us all aback and it was so awkward. I strongly suspect she was neuro-diverse, I know that's a common trope and diagnosis on mumsnet but she was so literal and weirdly obtuse about everything. Like she did not understand any social cues or niceties at all.
Before anyone jumps down my throat my DC is v severely autistic and we suspect DBIL is too so it's in DH family, we embrace it and all the quirks, hard as they are sometimes. This ex GF was something else though. DBIL is a v gentle person. His ex GF bullied him a lot, once told him his job was worthless. Like in a matter of fact way and did not see anything wrong with saying that to him. It made us all wince.
Your posts are making me wince in the same way. As PP have said, you need to reflect deeply.