wow! i have a good friend who planned her wedding after coming to ours, and a LOT of "her" ideas were more than similar to ours. but there was something different, like color scheme, location, etc. also she told anyone who would listen that she got the idea after coming to our wedding, so i always looked at it like a huge compliment, she liked our wedding SO much that she based her wedding off our ideas. i thought it was pretty cool!
but i can see that your story is not quite the same, especially given that her wedding is before yours and you have a lot of the same friends, and it will make your wedding seem like you copied them, and not vice versa.
i dont have any good advice, sorry, but i just wanted to say i feel for ya