Who Do You Think You Are?

Background: This girl, we'll call her Rachel, married her high school sweetheart, who happens to be one of my husband's best friends (they all went to high school together). The four of us hang out and double date all of the time. Amanda and I have hung out one-on-one a few times, and she even tried to get me a job at her company when I was unemployed and looking.

Story: Tonight I'm having a small girl's night in with a few of my girlfriends. I called to invite her on Saturday and got her voicemail. She is off and on instant messenger all day long at work (and sometimes even at home in the evenings), so yesterday morning I instant messaged her asking if she was planning on coming to my party. No response (even though it showed that she was on). I still have not heard anything back from her.

I don't mind if she doesn't come to my party - she's pretty shy and I understand that she wouldn't want to be placed in a social situation where she doesn't know very many people. I get that. But what I don't get is why she feels that ignoring me and leaving me wondering if she's coming or not is a good alternative to growing a pair and telling me she isn't coming. If you're not going to come, then just tell me you have something else going on or whatever. Who do you think you are that you can ignore people and dismiss them because of your own insecurities? I guess I thought we were better friends than you did. Fine by me. I don't need "friends" like you anyways.