It can work, but the way you’re suggesting is a bad idea. Do not get drunk to kick things off, you need to TALK in the first place.
The hardest part is kicking the conversation off I find, but if you’re just hanging out, being cozy with each other, a well tried classic is ‘oh my god I’m so fucking horny’, she’ll ask why, you say something about the fact you’ve been edging, she asks what’s that and you simply tell her about it. Which might then lead to reading this blog (pick out some ones you think they might like in advance perhaps and reblog them to another one of your own).
Just be real, talk to her about masturbation, what you do, what she might do. Have fun talking about it, she’s your best friend. If she’s being cool with it and getting into it, you could move it to talking about fantasies, share some each, maybe with some wine at this point, tipsy is okay once she’s clearly into the conversation, just to relax you both. Drunk is not.
Then, if your intuition says to try it, you drop in you’ve even fantasised about her sometimes. She will likely go crazy with curiosity, so make her work for it. Get her to admit if she’s thought about being with a girl, or you, or to tell you more about what she did that time.
Preface you actually sharing your fantasy with a real discussion about you being worried that it could mess things up. ‘Even saying it might make things weird, don’t you think?’ Make her think about if that’s true or not too. She’ll want to know anyway.
And then dig out the denial buddies ideas on here, see if she thinks it’s hot, and suggest you try it, but here’s a good trick. time limit it. ‘Want to try this for a week and see how it makes us?’
So yeah, it is obviously a risk but do it sensitively, and be really aware of how she’s reacting, not pushing her outside her comfort zone, and you might just discover she’d love it too. As long as your friendship is strong and honest enough for her to say she doesn’t want to, and you both be cool with that, then the upside is way bigger than the potential downside.
Let us know how you get on.