My friend has a calico cat and and a dog and all the sudden they stared fighting over nothing.they have lived together all their life and have never had a problem before. She does not want to get rid of them but she does not want them to get hurt. She tries to keep them separate but she has a small house and it does not work. She is reaaly stresse dout over this and I really wan to help her so please reply if you have a good answer

Sorry I spelled a lot wrong because I was in a hurry

If one or both of them are old now they could be temperamental.
It often happens with age. Since her place is so small she might need to get a cage for one or each of them and give them time outs when they fight and also cage them when she is not home to keep an eye on them.