a "virgin friend with benefits is an oxymoron. After the first night, she won't be a virgin. A friend with benefits is someone who repeatedly engages in sexual intercourse with the same person who, that person, told her in advance that he does not want to get serious about her but just to have ongoing , possibly infrequent but still ongoing, recurrent sex with her. A common English expression attached to such arrangements is no strings attached. One cannot engage in recurrent sex acts and stay a virgin. So a virgin friend with benefits cannot exist.

Unless you mean, and I realize there might be lost in translation issues in your post, that you want a friend with benefits who enters into that kind of arrangement as a virgin. But why would she? What would be in it for her? Can you explain?