To me, not "Test driving" a sewing machine before you buy it is like not test driving a car (or a motorcycle, but that NEVER happens) I would be stunned if she didn't let you power it up to make sure that things worked.
Turn the handwheel, it should feel smooth. If there are "lumpy" spots then it likely needs servicing (which you can do BTW)
plug the machine in, turn the clutch knob so that it's in bobbin winding mode and see how the motor sounds
put it in sewing mode, turn the hand wheel. If there are no crunchy sounds (needle striking something, etc), see how it sounds
inspect for signs of damage or abuse (bent or cracked parts - yeah, it happens. I had a guy ask me if I wanted a 15 that had fallen off a table and the main shaft was bent) - from what I can see, it looks good, but there are parts I can't see.
Check the wiring as I mentioned above
Check the light
The pedal is identical to the one on the 401, same adjustments if required.
She's selling this as a working machine, she should be willing to let you see that it's working.
The last 3 301s I picked up were all under $45 each. 2 in cabinets and 1 in a case. The thing is, I'm willing to do a complete dismantle and cleaning / servicing / oiling and replacing the parts required. One needed upper tension parts, one was fine, the other one needed bobbin case parts. If you want a machine that doesn't require 3 hours of that sort of work (besides an oiling which is regular - user- maintenance) when you get it, $150 isn't necessarily unreasonable.