Thanks again ladies.
I did end up talking to my Mom and letting her know that I found it. Honestly, like I said, she's like my best friend and I talk to her almost everyday (that was one of the big reasons this hurt so much). She was upset. She let me know that she had really wanted to come, and I told her that she really didn't show it and it really hurt me. She thought that I went out to get a dress to get "revenge" on her.
Either way, after a long argument over the phone, not to mention my sister talking to her, she finally calmed down and sent me a few text messages while I was at work letting me know that she was sorry for hurting me and giving the impression that she didn't care, and that she wanted to come in on Tuesday, take the day off and see the dress (and that she may cry).
So yah, after a heated evening, everything is good.
I'm starting thinking she's in the early stages of menopause... wow.