Random stat, but it fans the delusion in me so let me offer it up. You infer what you want out of it.
Since the beginning of 2012, the only player to whom Maria has lost (not counting W/O) that she has not beaten in their last meeting is Serena. In fact, we would have to go back to 2011 to find a player to whom Maria has lost and has not beaten since then.
Sequentially here are the last 5 players to beat her that she has not beaten in their last meetings with information about their last meeting:
1) Serena Williams RG F 2013 L 4-6 4-6
2) Flavia Pennetta USO R3 2011 L 3-6 6-3 4-6
3) Galina Voskoboeva Rogers Cup R3 2011 L 3-6 5-7
4) Virginie Razanno Fed Cup R1 2011 L 3-6 4-6
5) Greta Arn Auckland QF L 2-6 5-7
Thought it was interesting. It obviously doesn't take into account whether the subsequent wins against people not on the list could truly be considered significant "revenge" (e.g., For Li, does the Stuttgart F make up for AO SF?) as well as overall H2H (Vika), but I'd like to think it's a sign she (or most likely Hoggy since she's said before she likes to play by instinct) thinks about her game and losses to figure stuff out.
Also, not to get people depressed, but I saw this pic on twitter, and it just seems like the saddest thing ever, or maybe just for this weekend: