She didn't attack your sister she just wanted to get away from the dog. It is perfectly normal behaviour (I have the scratches to prove it!) - what the cat needs more than anything is reassurance and comfort, not to be banished to the basement where she is clearly unhappy.

You have to make sure that if the dog and cat are in the same room that the dog is under control - mine has to go on a lead at times to give the cat some peace, like yours he only wants to play