It's hard to say whether or not your friend will be mad. i guess you have to jugde it on whether or not she is usually a jealous person. I dont really have much advice, just see how things go later on. she might just need time to think about what you said and get over thr shock that she isnt the only one out for the guy that she likes.
While I'm here, i have a girly question too. There is this guy that I'm friends with and we both a have a mutal friend. When she found out that i liked him, she told me that he was gay, but i know for a fact that he isnt because he told me that he isnt, and all his freinds say that he isnt. Plus, she'll intintally mention her talking on the phone with him or going out with him to make me mad. she does not like him that way I know. why would she be trying to get me away from him?