Re: but did she actually entertain romantic feelings before Lydiagate?

I guess it depends on what you mean by entertaining romantic feelings. After his visit she can’t decide how she feels about him but when she thinks that her power over him is sinking it clarifies her feelings and she feels she "could have loved him".

I would call this “entertaining romantic feelings” in the sense of having them over for tea and trying to decide whether you want to be further acquainted with them or not. But, if you mean a burning desire or the stuff of romance novels then no.

IMO she was on her way to falling in love with him and if she hadn’t been interrupted by Lydia’s letter and spent more time with him she would have come to love him.