There has been a good deal of discussion lately about "trip charges;" that is, charging, say, $35 just to come out. This approach has its' benefits- not the least of which is that you get the credit card info in advance; no-show customers do happen!
Once you're out there, maybe it is a simple five-minute job- or, maybe, it's not. You won't know until you're there. And, con't forget, the customer is an unknown at this point. Mean, greedy, young jerks sometimes grow into sweet, innocent-looking, old jerks!
You might suggest she call Sears- she'll find out they have a pay-in-advance policy as well. "If Sears does it, it must be OK."
Your time is money, and gas is too expensive to waste.
I also have had great feedback, after the job is done, when I knock a few dollars off the bill (on my own- if they start the 'hustle,' the price starts climbing!)