How can I help this girl?

[Alyssa]

I would just tell pull her aside and tell her about it. I think you are doing the right thing by trying to warn her before it really gets out, but since you say a few people already are aware, I am sure it will spread fast. It would really awesome if you told her like pronto so she has a chance to get it down before too many people see! I know its likely awkward for you, but believe me I am sure she will be very very thankful. Just say "I just wanted to let you know I have heard around school about your twitter account and I wanted to give you a heads up before too many people see it"