Intermittent not starting iusse, possible fuel problems?

I had a new tank, and a fuel pump put in it just recently. Lately it’s been acting up. It started earlier this week when my wife took her car to Walmart. She went to put the top up, and out of the blue, it wouldn’t start. She got the top up, went into the store, and came back out to try to start it again. It wouldn’t start, and acted like it wasn’t getting any gas. Wouldn’t fire at all. By the time I was nearly there to pick her up, it started. Took it to the mechanic, and in the two days he had it, it started every time they tried it, without fail. We brought it home, and a couple days later it stalled on her way home. A customer of hers stopped to see what was going on. He used starter fluid on it, and it stayed running for short while but continued to stall out. I came home from work and went up with the intentions of towing it home, but she tried it one more time. It started back up, and she drove it home, which was about 7 miles distance. It’s been parked for the last few days. Lost on what the problem could be.