she stays with your friend, she will be in a strange place and will be with a strange new creature! however, she could be supervised better than if she is at home alone. and have some company.
so ...again my first choice would be to find a house sitter who would live in your home while you are away.
my second choice would probably be to try visiting your friend a few times with your cat to see how things go with her other cat and her home.
last on the list, i guess, would be to leave her alone for that length of time unless the person coming in can spend time 