I like her, she works in the office with me, and we've known each other for a month. I had already been hanging out with her and some friends. We have confidence, but I have not exposed my romantic intentions with her. I want to go out with her to talk and drink some beers, after office, create an interaction of only her and me, and be able to take it to the romantic plane.
Once happened with a girl in a similar situation, where I invited her and she then took a male friend and I could not be alone with her.
What is the best way that I can invite her without being explicit that I want to be only with her since my intentions are romantic?
Notes and clarifications
I don't want to be explicit (not showing that my intentions are romantic before going out). I think that it will create tension with her, and I don't want that.
I don't want to represent the outing as a group event, I want to represent it like a relaxed talk with a colleague.
I expect that she feels comfortable in the conversation, and then making little steps of closeness, turn in a romantic interaction plane. And see what happens, only then... If she refuses my intentions, I will accept the decision and move on.
In conclusion I want to "make a move", to transition the relationship.