This translation doesn't seem right to me. I would either say " She had forgotten the keys" or "she had left the keys at home"
I agree, I would transalte this sentence as 'she had left the keys at home'
I don't see any problem with it. "i forgot my keys" "Where?" "At home" "You forgot your keys at home?!"
Unusual, and far-fetched: "Mum had lost the keys on the hillside and thought we were stuck. She had forgotten the keys at home. It was a duplicate set. I went back for them". Possible.