I agree with many of the posts and one that stands out is Angie's.. PANDAS.. when my son had Meningitis and thankfully recovered, he had anxiety thereafter for about 6 months.. E.g., we'd be at a gas station and he'd insist that his dad roll up all the windows and lock the doors. Additionally, he kinda had ticks (which is apparently common after an illness) his were such that he would get this kinda twitchy feeling along his scalp and on his side. I was worried sick.. but the doctor said it should go away , which it did..
I think one good thing to do whether kid or adult is to do a water cleanse after illness, have her drinks lots and lots of water to get rid of the meds in her body. Also, certain meds as noted below can cause depression, for me, Benadryl so upsets my system... After taking it, I just feel angst and then depressed. of course, I no longer take it..
Also, watch her diet, could be at 10, when allergies can begin to manifest themselves are starting to reveal themselves symptoms, which depression can be of many.. If she doesn't continue to get better, I'd get a second opinion.. When my son developed that anxiety over the gas station, I took him to my former therapist and before I could even say he had been sick, SHE said... was he previously sick and did he have to stay in the hospital... so apparently it's common to have mental and emotional side-effects after being physically ill...
keep us posted and good luck
blessings