Ford - Focus :: 2000 2.0 - No Response Intermittently When Depressing Gas Pedal

I bought my girlfriend a 2000 Ford Focus with 150k Miles on it to drive for the summer in Oregon. The car is physically in great condition with no noticeable leaks on it. After a week or so of driving, my girlfriend complained that a couple of times she would be driving the car and while going up a hill "nothing would happen" sometimes when she punched the accelerator. I asked her if the engine revolutions were going up and if the engine made a "vroom" sound (to try to see if the transmission was slipping) and she said it did not.

On a long trip driving from Seattle to Portland, she was driving again and we were climbing a long hill and she suddenly complained that "nothing was happening" when she punched the accelerator. She panicked and pulled off to the side of the road quickly. There was no shaking or vibration. I did not hear the engine wind up when this happened... so I am assuming the tach was not going up when she depressed the gas pedal. I opened the hood and looked inside and seeing nothing obvious, I switched to the drivers' side. No codes were thrown. I drove the car up the rest of the hill and to a flat area and we let the car cool off for a few minutes. I drove the car for the next 75 miles to Portland without event. When we got to her grandparents house, I changed the spark plugs (which were pretty fouled up), and changed the fuel filter (which actually looked pretty new.) and it seemed to satisfy her for awhile. Being that I havent experienced the issue, I just assumed she is not used to driving a small hatchback with a fairly wimpy engine.

In the meantime I had the entire front end redone, control arms, etc and alignment because she had had a slight shake...which is unrelated here but i figured I'd mention it. So, the other night she calls me on the side of the road, slightly shaken. Her latest incident was as such: at the bottom of an on-ramp to the highway, she punched the accelerator and "nothing happened" when she hit the pedal. This time the check engine light briefly came on, and the "OIL" light came on. She was able to pull off to the side of the road somehow and then pull to an exit. She turned the car off and let it sit for 5 minutes.

Here's the weird part: She started it up and claims she put it in "Drive" and pressed the gas pedal and nothing happened and the car actually started creeping backwards. She hit the brake and turned the car off. She started the car and drove away 5 minutes later without incident and drove it 20 minutes home. She said her gas was very low when this happened, close to the gas light coming on.

She took the car to a reliable mechanic in seattle the next day, and they said there was no issues and they thought the car was actually in great shape. Unfortunately no codes were logged and no codes have been logged at all! My only other weird observation about the car is that the tach seems to fall kind of quickly after acceleration... almost comically compared to my volkswagen 1.8 which has a gentle rise and fall to it. It kind of bounces up and down but the ride is smooth. Random, but i figured i'd mention it

Should she just make sure to keep the gas level above low/empty?Should a fuel pressure check be on the docket? The previous owner claimed the timing belt only had 25k on it, but he could have been lying.