Car won't start when it rains

I have a friend whose 2000 Buick Regal cranks, but won't start when it raining. She has taking it to her mechanic several times, but the problem is still there. I know the fuel pump was changed, that didn't help. She has a running tab with this guy, owes him a couple hundred still. I would like to help her before that tab gets out of hand. There is no fault codes, no check engine light even when it doesn't want to start. Do you guys have any ideas?

my first guess would be spark plug wires

I did some research on this site, that is what i was thinking. I'm going to ask her if all that was changed. Could there be any sensors that would cause it to not start? Now the mechanic is saying it the computer.

Check the grounds on the car. If the ground is rusted it will be worse when the weather is wet and won't ground properly. Clean the battery terminals and the ground connection at the block. Also check the ground to the computer it will do the same thing!