I cant' see her as a symbol of "evil"... that is IMO far too strong a word, for her selfishness and spoiled ways.

I think that she would be - indeed we know she is jealous - when she fears that Edmund might find ohter women attractive, but I'd say that if she were married to someone of her own London set, she would not expect more than the appearnace of fidelity...and indeed if she made such a marriage and her husband was givne ot open flirtation or more than that theres not really much she would be able to do about it.

Possibly she HAS unconsciously been drawn to Edmund because she knows that he would be more faithful and decent than most of the men she knows... but all the same, there are such differences between them that it would be I think a difficult marriage with both of them finding it hard to understand the other. I think that she would find him boring at times, and that she'd be the one perhaps who was flirting, and wanting to go to London a lot or live there, and that Edmund would be horrified at her lively behavour and flirtatiousness even if Mary "meant no harm" by it...