I think when she says, she regarded herself with an interest. She means that she is interested in Darcy perhaps love him. Then by saying, if not quite so tender, maybe she means she has not always been esay on Dracy or that she did not fall in love with him as easy as Binbley and Jane fell in love with one another. and the last part may mean that what she now feels for Dracy is no less then what Jane and Bingley feel for one another even if Elizabeth wasn't always in Love with Darcy is it no less just because Bingley and Jane always have been.

I'm not sue if what i said has made sense but i seem to understand it.