I'm Neal and I am here to assist you. Only accept when you are happy with my assistance. If I can't help I will open your Question to other experts.
She should go to a parts store and ask them to read the codes, they will do this for free and it could just be something simple like a loose gas cap which is the most common cause for a check engine light.
If it is more serious she should just conside returning it, in most states you have three days to opt out of a sales contract.
It is not a bad car but if it has issues and dthey sold it to her that way, she needs to just back out of the deal asap.
Let me know what the codes are and I will help you determine what is going on.
There are several things it can be, from the need for a tune up to more major problems. Here is a list of possible causes, but the fiirst thing to do is to change the plugs and see if it resolves it.
A misfire code may mean that one or more of the following has happened:
So I am guessing from all the possibilities, we need to take it back and have them look at it?!