Geo Prism stalling out

My daughter has a 1990 something standard drive Geo Prism and when she drives home from work she takes the Mass Pike for about 20 minutes and then weaves thru fairly intense Boston traffic. The car keeps stalling on her in the local traffic, but our mechanic can’t replicate the problem, nor can he discover any problems when he goes over the car. It doesn’t happen in the morning when she goes to work. Does anyone have any ideas for what would cause this?

change the fuel filter