I am sorry that your mom is making you feel guilty about that. At the end of the day, you have to do what makes you happy, and not what makes everyone else happy.
Like you, my grandpa will not be able to attend the my wedding due to his age (he will be 89 when I am to be married..closer to 90 actually) I feel a little guilty about that fact that my grandpa wont be able to make it to the wedding but at the end of the day, all he wants for me is to be happy and do what makes me happy.
Hopefully with a little time your family will be able to see that you are happy with your decision and that is all that matters.