Honestly, I don't consider either woman to be among my closest friends, but Linda clearly feels otherwise, which I do feel a little guilty about.
Why do you feel even a little guilty ?
It makes me feel as though there's an inequality in our relationship, but I can't change how close I feel to her.
OK, first thing you have to do is get over any guilt feelings you have. Guilt = you've done something wrong and you have not done anything
wrong here. You cannot control how Linda feels and it's not your responsibility to. And you have your own feelings which you have a perfect right to.
Not only should you not feel bad that she wants to be closer friends with you, but in fact, I'd start pulling away from her. The whole idea of her wrangling you into a plot to trick Jane, thus putting you in the middle, is abhorent to me and I'd want to distance myself from her because who knows what trick she will pull on you
if she feels the need.