Hi.
I'm sorry that your friend is trying to steal the student election through bribery. It's not right, and it defeats the purpose of having a democratic student government. Unfortunately, "people" are people and they can--and do--cast their votes for any number of reasons that may or may not have anything to do with who is the best for the job.
There are a couple of things you can do to try and win the election. One of them, of course, is doing some cheating of your own. Considering how upset you are by your friend's behavior, I'd say this probably isn't an option. It may be better to lose this fight and maintain some of your standards than to win it without any ideals.
I'd also suggest speaking to your friend. Maybe she doesn't realize that her behavior is 1) improper and 2) making you angry and upset? Perhaps she'll think twice about her tactics if you confront her.
I think the most important thing you can do is focus on your own campaign. You can make sure the people you go to school with understand who you are, what you hope to do for them while in office and how hard you are willing to work. It might be that when it comes to actually voting, people will vote in a fair way--even if right now it appears they are responding to the bribery.
Perhaps you could also look into your school's election protocol. Although nobody wants to be the "tattletale," your friend may be violating school guidelines and could be disqualified from the election. If she's not, you may want to take a look into creating some new guidelines for your council that prohibit blatant attempts at bribery.