Not trying to pick a scab here but I think the customer is trying to communicate her perception of the value to fix by giving you a time frame. My response would be to give her your estimate to fix (sticking with the T&M method here) and ask if she wants to spend that amount on it. If you don't have enough information to give a solid estimate, tell them that and offer to investigate for X dollars in X time. If at the end of that time, you don't have a fix, you will probably have better info to set an estimate for completion. If not, wash, rinse, and repeat.