It sounds like you have an electrical problem.
Make sure that the ignition components have clean/tight/ good connections.
Especially check the alternator connections.
How did this problem begin?
how many miles does it have?
did she explain what happened when this started happening?
like I said, check for any loose/damp connections at the distributor/ coil and especially the alternator connections.
If that fine, then try spraying some engine start fluid into the intake and see if it helps. We have to find out if this is a fuel or ignition/electrical problem.
this is likely an electrical issue, because you mentioned that the dash lights flicker when it acts up.
About how long after the car is started does it start to act up?
also, did you make sure to get the same amp rating of the old alternator?
It is likely that they may have given the wrong amp rating and maybe it puts out enough power when it first starts, but once hot it doesnt provide enough power thus creating your problem.
np, let me know your status once you have things checked up.
I would test drive it around the neighborhood till the engine reaches operating temperature and see when it starts to act up. Note the rpm's, where the engine temperature is at, and if it does it while accelerating/decceleration or when you have the brake depressed.
Now, we need to make sure that this isnt being caused by the fuel system(just to get it out of the way). What you need to do is, spray some engine start fluid into the manifold and then try to start it. Pay attention to how the engine responds to the fluid. If it sounds like it helps, then we can get it out the way. If not, then thats what we need to focus on.
I was just wondering, if you have a timing light? with a timing light, you can check if there is spark when the engine is giving up. You would hook it up the same way as if you were to check timing, but you wouldnt be interested in the timing. You would just watch for the flashes.(its ok if not available)
also, after or before you do the check with the engine start fluid. Check for vacuum leaks especially around the intake manifold and throttle body.
I was also wondering, if you checked the electrical connections at the ignition coil, distributor, and alternator?if not, do so.