My friend is coming over and I'm a girl and she's a girl and I kind of want to experiment with her and I don't know how to ask her. She would probably be cool with that because we are really close friends, but I just feel awkward, so any suggestions?

Bring the topic up carefully and very casually. Just talk about how you saw/heard/known about something along those lines and that you have been curious about it for a long time. Then ask what she thinks of it. If she's totally grossed out, then you can just shrug and be like "well whatever, it was just a weird thing that came up in my mind." But if she's like "hmmm...that does sound kind of interesting" then slowly take it a step further, asking if she wants to try it sometime.

If she reacts like "no way, that's not for me" then back off and change subjects like "well I'm just wondering if there was people who actually wanted to do that. Anyway...." On the other hand, if she goes "yeah, I'm a bit curious about that" then ask her right off the bat. "If you're so curious, would you like to try it with me?" kind of thing. But don't beat around the bush about it. Just say it straight and to the point. If you just kind of imply it and then you kind of don't, it might send her mixed signals or it'll just be plain awkward.

In situations like this, be sure to be respectful and considerate of your friend's feelings and thoughts. If she says no, then it's a no. Back away from it and start talking about something else. Don't make her feel bad that she didn't want to do it with you (if she does say no) and just make sure that you guys have no hard feelings afterwards. It sounds simpler saying this than actually doing this so rehearse different scenarios in your head and try to think of what you would do in those situations.

Anyway, I do wish you luck on this. Whether it's getting her to actually do it with you or not making this sound awkward.