I'm so sorry Sara. I'm totally seeing some of our own experiences in yours and it sucks. Your mom finding a convenient excuse not to go is just so mean and hurtful -- DH's mom and brother did the same thing to him. It's your wedding, for goodness sake! I don't really know what to say about that other than it is really hurtful of them.
As far as the future in-law situation is concerned... I won't go into much detail, but our in-law situation is not the best either! DH is no longer speaking to his mom and brother because they would not accept me (there are other things behind it too though), and right now I am trying to get DH and my mom on good terms. I let the tension between DH and my mom go hoping it would work itself out, and let me tell you it most certainly didn't, and only made things worse. Much worse. Now I am sitting here wishing that I had spoken up for my husband in the beginning, before we got married. I know the situation is a bit flip flopped since it is you having problems with Shane's mom, but I really hope you guys can get this talked out instead of letting it fester like I did.
I've found that if there is one thing weddings are good at, it is hurting people's feelings!