The problem you have perhaps not considered is that this lady is almost certainly going to be claiming Local Housing Allowance. A guarantor is not to be confused with a tenant. It appears you are not conversant with such a situation and if you don't fully understand the implications then perhaps you might want to look for another tenant.
The advice I give should not be construed as a definitive answer, and is without prejudice or liability. You are advised to consult a specialist solicitor or other person of equal legal standing.