Linda and the Engagement Party
I can understand why Linda was upset that Julia said she could throw her an engagement party and then changed her mind (but to be fair, Julia didn't seem to realize that Linda felt really strongly about it and it was more than just one of her apparently endless whims) but it's Julia's wedding. She's the one getting married and Linda kept insisting and practically forced Julia to agree to let her throw the party even though she knows her idea of a good time and Julia's are very different? Then she won't come down to her own sister's engagement party because she's pissy she didn't get to throw it? It's not about her. And it's not like the party was put together in one day anyway. She had time to get over it.
She was just so immature and badly behaved in this matter and it made her more unsympathetic than the romantic heroine should be, especially since the narrative seems to agree with her.
If it were Linda's engagement party and her family took her quiet little party and made it a social climbing shindig that would be different but it's not. It would be one thing if Julia had asked Linda to throw the party and then took it back but that didn't happen either. It's Julia's engagement party and she has a right to whatever kind of party she wants.
And her avoiding the party wasn't just being childish. She was actively spoiling the party for her sister, the one the party was about. But no, the movie thinks Linda is being warm and human and better by this petulance. Instead of talking Julia up to Johnny's parents, she should be at the freaking party!