You need to listen to your girlfriend, if she says she doesnt want to do it dont push her. Dp with toys is one thing but a totally different thing with two males, having fun with others is great but if it hasnt turned into a full sexual experiance i would take that as its not going to happen. And seriously getting her drunk is not the way to go, to decide to swing she should be sober as under legal terms she would not be capable of making a decision of that kind let alone anything else. It may be your sexual fantasy to have a threesome but it doesnt sound like its hers, and pushing her into it could cost you your relationship.