You're probably tired of hearing it but ... use lots of lube! For real, dude. It's super helpful.
As most others have said, just start small with your fingers and really work things until she's ready. It'll probably hurt a little the first time. Just go REALLY SLOWLY and keep checking in with her to make sure she's doing alright, giving the OK to go forward, etc.
I'd say start with a toy first and let her use it on herself. It'll make it easier because she can control exactly how fast it goes and how deep, etc. It'll also be hot to watch her ;)
Thanks for the advice! And oh yes,always fun to watch hehe