OH boy!! I wish I had some advice for you, i just wanted to respond because I have an 18 month old who still uses the bottle for falling alseep at nap and bedtime. Granted she is younger than your LO, but it is still an issue.
I can however, give you my opinion...i think if you really truely want to get rid of it, your idea is great. make her a part of it and so she knows it's the end of the sippy! BUT...if it really doesn't bother you, I would explain to her that school is not the time for sippy, but she can have it when she's at home. Who knows, maybe not having it at school will help her decide for herself that she doesn't want or need it at home.
That is my plan for my daughter. I feel when she is ready to quit the bottle, she will let me know in her own way.
Good luck, and let us know how it goes!!