D.S.
The MMR is rough on their immune systems - my older son had a similar reaction to it, and I swear, I think he was 'off' from it for about two weeks. I actually requested that it be split up into three seperate shots for subsequent doses, which helped a lot, but I don't think that's available anymore. I also gave him lots of lavender-scented baby oil rubdowns, massaging him and that would help.
Just try to keep her comfortable. Her immune system is working overtime right now trying to make all those antibodies, and that's what is causing the swollen glands. Reactions to vaccines vary, and can be really scary (we had a few other odd reactions that were deemed "normal"), but the ped has likely seen it all and will tell you not to worry. Hard to do, but in this case, they're right.