Tenant Applicant with Cosigner who is retired - accept or deny?

[Brian Green]

I have a unique situation with a tenant applicant for one of my rental units. On her own she fails to qualify for the apartment because of insufficient income but her mother is willing to co-sign on the lease agreement. Normally that would suffice and allow approval but the mother is retired with only $45k in assets in the bank.  Additionally she has some spotty credit history with some late pmts on credit cards and some closed accounts. The mother has just over a 600 credit score which is our baseline requirement and the tenant applicant has slightly higher but again not enough income. 

How should I assess this application for tenancy? Deny or Accept? 

There has been lots of activity on this opening but this tenant was the first to submit an application. I have plenty of time to locate another qualified tenant if I pass on this applicant before any vacancy starts to hit my bottom line. What do you think?