Look at this blog it will help you to learn more about your situation.
I've got most of my answers there as well.
Yes, in some cases co-signer can allow you to "purchase more house".
In the event that their salary is low and they have high monthly obligations they might force you to buy less of a house....so it all depends on the co-signer, his/her financials and the deal itself.
Upon a more careful review of the situation, I can make an opinion whether it's a good move or not....the current info is not enough.
The downside for the co-borrower is that she is also responsible for the mortgage.
My suggestion is to purchase what you can afford...in my buyer's case she has actual income disallowed so she felt comfortable adding a co-signer.
If you have any other questions, please feel free to drop us a line or give us a ring.