DD, it sounds like maybe she's been feeling well enough to possibly overdo a bit. Remember, she's been less active for a while, so she was probably a bit out of shape. Enough so that she tired herself out when she started feeling better again, maybe? It might be that after a few days she'll recover and start being more active again.
"We are--each of us--dying; it's how we live in the meantime that makes the difference."
"It's not what you gather, but what you scatter that tells what kind of life you have lived!"
"Be kinder than necessary, for everyone you meet is fighting some kind of battle."