I don't know what to do and need your advice...

Ok- here's the situation. My FH and I wanted to do a joint bachelor/ette party and planned it out and 11 of our 12 ppl finally said yes (after changing the dates around a few times). Anyway, that's kind of irrelevant I guess but I called the last BM this morning and she left me a message this evening to call her back so I did. I told her the day/date and time and where it would be and she just kept saying 'UUH- UUM- uuh...' like she was stalling to figure out an answer. She then wanted to know when it was, why we were doing it, who was going to be there, how much it would cost, etc... and then said 'I think I'll pass- maybe next time'. Maybe next time? How many bachelor/ette parties does she think we're planning on having??!?!?
That was just kind of the straw that broke the camels back. She's the only one in our BP that didn't show up to our engagement party b/c the invitation 'got lost in the mail' and never made it to her (even though my mom called her) and she's done nothing but ignore my calls and take forever to get back to me and be negative and BLAH about EVERYTHING. I don't know what to do b/c I'm a COWARD (and I can admit it) when it comes to telling people how I feel but I just don't know what to do anymore. I was just crying for the past hour and a half and I can't sleep so I figured I'd turn to 'my brides' (and grooms). I know some of you have had some similar situations and thought maybe you could enlighten me. If nothing else, thanks for 'listening'- sorry it's so long.