Was this mother out of line?

My son is 15 and his best friend's ssiter asked him to Winter Formal. I know the girl, I know the parents and I thought it would all be smooth sailing. But, from day one, the mother didn't communicate ANYTHING to me. She didn't tell me when the dance was, never replied to my texts about what the plans were, didn't call when she told her son she would call me, didn't inform me of the transportation situation, the flower situation or what the kids were doing for dinner (she KNEW this was my first time planning a formal for my kid.). The final straw was the parents of this group (4 couples) apparently made plans to hang out, have appetizers at one of the parents' houses then getting pcitures of the kids before they left. My husband and I, however, weren't invited. I found out when this woman's ex hsuband - who provided the transportation - asked if he was going to see us later. I had NO idea what he was talking about. I ended up crashing because I wanted pictures of my kid and this mother looked surprised and nervous to see me. The other parents didn't know me and were prfectly nice, if not a bit confused by my presence so late - pictures had already been taken. I was completely hurt by this mother's treatment of me and I have no idea why she would do this! I provide ALL transportation for her son (at NO cost to her)! I thought we were friends and I seriously have no reason to believe I made her angry. She didn't seem angry at me - more nervous. Like she had just completely forgotten me or something! How wierd is this? I know she has some stuff happening in her life and I gave her the benefit of the doubt right up until I fould about about the parent get together. I felt completely disrespected by that slight. Plus, I go NO thank you for getting the flowers - from either mom OR daughter. Now, I wonder how I'll be able to deal with her. Should I say something or should I wait for her to do it? How wierd is this? Moms - how would you feel in my shoes? What would you do? I feel I'm owed an apology, frankly. Not to mention an explanation why she felt the need keep me away from this whole thing. I understand it's a bigger deal to the girls but this was my son's first Formal and she knew that. It was so hurtful and if she was a peron I never had to deal with again, I'd be able to get over it, but her son and my son are best friends. My son knows I'm angry but this isn't for the kids to be in the middle of. It's just so awkward.