Replacing Maid Of Honor

I need some advice. I am from Illinois, but live in Canada. I am planning my wedding for September in Illinois. My maid of honor lives in Florida now, but we grew up in the same town and have been friends since Jr. High. I asked her to be my maid of honor a couple of months after I I was engaged. Last month I went home to Illinois and bought my dress and picked out the wedding flowers. So now I need my maid of honor to buy her dress. I have the style and color picked out. The problem is I have called and left messages for her to call me so we can talk about the dress and color. I have even emailed her and told her on a phone message to check her email. Either way, she has not responded back. I am starting to feel like this is a one sided friendship and that she doesn``t care about being in my wedding. Would it be terrible etiquette to ask another friend, who has been there for me (even went dress shopping with me) to be my maid of honor instead? Any advice would be appreciated.