I am fond of men of size, and it's been my personal experience that sleeping with a partner significantly smaller than my husband can be a problem and bodes ill for the sex life I have with the other partner. It's not a length issue at all, it's a girth issue. I am used to well-above-average girth with my husband.
I have a past partner who was very small, girthwise, and our sex life was always problematic for me because of this. I simply could not feel him much. I tried not to let him know that this was the case because it was not something he could help, and I loved him. He figured it out anyway though, and it was a significant part of why we broke up after two years. His feelings of inadequacy took over and made him very, very angry at me, which was expressed with a whole lot of passive aggressive behavior and dishonesty, egged on by a jealous metamour. Bad scene. If I encountered a partner who was unusually small again, I would likely end the sexual relationship right away and transition things to friendship if I could.
Sleeping with a partner who is significantly larger than my husband, though, has never created problems in the sex life I have with him. I tend to enjoy the new partner's size a lot, but I'm still quite happy to be with my husband too.
I think it depends on the lady. Some ladies don't even like very large men. Some ladies do. I think anatomy has a lot to do with it, although there is definitely a psychological component too, at least for me.
I'd say, if she is enjoying sex with you now, I don't see why that would change.