I trust your judgment and value our communication. You need to be prepared for her answer. It takes a lot of courage to ask, and asking is the only way to increase the likelihood of getting what you want. You know, there is something I'd like to talk with you about that makes me feel kind of awkward, and I hope you will hear me out before you react. Then tell her what you were thinking about.
Friends usually respect and depend upon gentle honesty.
You can skip the potential pitfalls of sex with friends by looking for a brand new partner who's not a current friend. Alice agrees with you.