Can feeder fish harm/kill my axoltl?

i had a black female axolotl, her name was herbit. herbit was about 1-2 years old. i got her off my sister at about 6 months old she was skinny we thought it was normal. my local pet store (where we bought her) seemed clueless when it came to axolotls even though they buy off breeders and sell them, she hadnt been eating properly for the last 1-2 weeks i was worried so i bought 5 feeder fish from my local pet store (last week) expecting her to eat them and regain her appetite, i put 2 in her tank and left the room (she would never eat them in fron of me) i came back 2-3 hours later one of he feeder fish was eaten and the other was still there (i took it out) but my axolotl wasnt ok any more, she couldnt stay on the pebbles or even close to them if i helped put her close to the rocks she would float up to the top very quickly and then sway from side to side (even flip a whole 360) and then settle floating right at the top to the side her skin would be a few millimeters out of the water and if i touched the water next to her she would swim away and then sway and settle again. after a whie of worrying and internet searching i went back and noticed that all her toes on her left back foot were missing, i didnt know what to do and couldnt find anything online. A painful 4 hours later she died. im now looking to get more axolotls and dont want this happening again, im not buying from my local store as they have no clue! can you please help :)