Help! I just adopted a Finch !?

Today my sisters 7 year old kids went to the petshop and brought a finch and my sister wasn't expecting it, her cat tried to eat it and it was in a box for about an hour. I went to her house and firmly stated it shouldn't be living in that enviroment, so she let me take it home. Good thing I had a spare cage! I have a lot of experience with birds as I've owned my 2 ateils for a while now, but I have never dealt with finches. It was quite stressed for a couple of hours but now it's feeding and seems quite relaxed. I have heard that finches need the company of another finch or canary ? I put it in my spare cage as they feel intimidated/scared of birds bigger than them, so putting them in the cage with my teils is a big no no. Should I buy another finch to keep her company ?.