take a deep breath and relax
This is about tactics and training, and yes you're right to bring the hypotheticals for us to kick around with you. Thanks for posting this; seems that lots of us find gas stations to be potential problem places.
Before I got my pistol, but when I was seriously considering one, I stopped one afternoon at the convenience store for gas. NOticed an old guy standing around in front of the place, looked pretty down and out. Aaron, my youngest son (16 at the time) got out and was going to pump the gas. He went in to pre-pay and when he came back out, the guy followed him over to our car. He wanted money, had a long story about brain surgery and how he couldn't work now. Aaron gave him some as did I and then he looked at me and said "nice car, what year is it". Mind you, Aaron, who is over 6 feet, was standing right there, but I too had one of those "what if" moments and without even thinking, reached over with my right hand to my left side as IF there were something there. He backed up pretty quick. Said thanks turned, went into the store and bought cigarettes with his "I'm starving" money. He was probably harmless from the get go and I just scared him because I was acting weird! But still, it was one of the things that tipped the scales toward getting a gun at all.
Now, for your scenario, and reflecting on my own (and other things like it): part of what we have to do is be really calm, cool and collected when we are carrying. For ME certainly that means not making any assumptions too quickly about another person based on appearance, etc. I have the advantage of having a teenage son (same one as at the gas station) who has an assortment of friends whom, well, you would be nervous about at the gas station if all you knew of them is how they sometimes look. Hey, you might even be nervous about my kid. But it wouldn't be necessary, and it wasn't with the kid at the gas station you met.
I wouldn't worry about "watching out for her" when she pumps her gas. She's a big girl. You're there if necessary, but getting out and guarding her when she pumps the gas is unnecessary. If the neighborhood's THAT bad, plan to get gas at a nicer place. I myself need to just watch my surroundings, not be quite so on edge as what you're describing.
One other question: if you can't see well enough to drive at night, why in the world would you carry a weapon at night? How could you see well enough to aim and ENSURE that your bullets would hit what you wanted them to? Just a thought to consider.