OP, guide her to the MMO Warlock forum, I'm sure she could get a lot of tips and help with her spec, gemming, enchanting, reforging etc. Cause something's clearly wrong, when she's doing so low numbers. As others have said, most classes have changed a lot and if you don't stay on top of the changes, odds are you'll keep falling behind.
About benching her or not. It really depends on what type of mentality your guild has. I mean, sure you've been raiding together for a long time, but even friendships have their limits. Cause in the end, her performance is holding the rest of your guild back. As someone else pointed out, most of your raiders could have performed a lot better, so maybe they shouldn't be too quick to point their fingers. But someone will always be bottom and if you're bottom by miles, people will notice and start playing the blame game.
I'd too advice you to talk to her. Cause surely she must be aware, that she's not pulling her weight. Guide her to MMO, teach her how to use Simcraft maybe? I mean, with Simcraft she can see, what sort of numbers she should be putting out. Sometimes that can be an eye opener for people. In the end, I'd say that one person holding 9 others back isn't worth bringing on progression fights at least. Find someone else and bring her, once you get better gear and can carry her. That would be another option.