It’s not up to you to decide
You’re missing the whole point of a cosigner, which is to have someone with good credit to offset your credit problems or lack of credit, and share responsibilities & liabilities in paying the loan.
So you see, someone with bad credit simply cannot be a cosigner. A cosigner with bad credit has no value to the creditor.
The second thing to understand is that the decision is not yours. If the creditor approves you w/o a cosigner – good for you. If they want a cosigner, chances are that your mother won’t qualify.
What you need to do is to try and pass it yourself. If they’ll insist on a co-signer (chances are that they will) then you’ll need to find a cosigner with good credit in order to get a student loan.