I created two young men and moved them into a house near Mary's. That way I figured Mary would be one of the sims welcoming them, and in fact she was. She took a liking to both of them, but my preference is for one of the two. After she had established herself enough to be gaining friend points I went back to Mary's house and had her talk to my preferred guy on the phone. Later I had her invite him over. Both activities led to the development of friendship and a door opened for more. There was quite a bit of difference between the way Mary and Leo acted in the hot tub and the way Mary and Benjamin were. Benj is just too standoffish. I prefer my guy now.
The next step is to see if we can blossom this into love and get Leo to move in, marry or not. Then Mary can keep up with her career, get pregnant, and he can stay at home maintaining household friendships and keeping things clean. I don't know what pregnancy does to persons in the criminal track. I don't think it would go well with being a cat burglar but maybe the next level? Which, I know now (I have the book!) is counterfeiter. Should be able to do that with a baby in there.