ok this hasnt happened to my thirdgen but it could I suppose (this is really about my moms 98 olds intrigue, shes on the other side of the country so I cant investigate first hand, only what the "mechanic" tells me) lets say the car has been driven for awhile like this, is the tranny shot or can we just drain it and hope for the best?

I assume the cause for this has been sorted? ie the only way water can get into the trans is through corrosion of the cooler pipes inside the rad. This turns the trans fluid to milkshake. Result? Goodnight vienna to transmission...sooner or later. Most likely sooner. Draining it won't hurt, but if it has been driven for some time, it won't help either. May be worth a try though. As long as you can pump it out of the converter as well.

Good luck.
Andy.

yep, radiator...

does the fluid in the converter eventually intermingle with the rest of the trans fluid? if so can you just drain it , drive it a bit, drain it again, etc till its clean?

I imagine pumping it out of the converter is a nightmare

Best bet to flush it would probably be have it towed/trailered to a shop that has the pump to do it, that way they can evacuate 100% of the old stuff.

Hopefully it plays out for the better, but not sounding good if she put some miles on it.

Your Mom's car seems about the right age for this. Here's a common fix:
Get the radiator repaired or put in a new one;
Get a case of tranny fluid, 5' of fuel line and a 5 gallon bucket;
stick one end of the fuel line over the end of the hard tranny coolant line that runs to the new installed radiator and the other end of the fuel line into the 5 gallon bucket--put a funnel into the little tube where you check the fluid level, because when you start the car the old fluid is gonna be pumped into the bucket and you'll have to pour tranny fluid as fast as it'll take it into the funnel.
This method replaces all the old tranny fluid, even in the torque converter, in about a minute. It's best to have someone in the car shifting slowly through the gears with their foot on the brake to fully flush the valve body, too.
When good, new fluid starts pumping into the bucket, shut off the motor and hook up the coolant line to the radiator, then get under there and put on a new tranny filter kit and clean out the pan because water will collect at the bottom.
Be sure to check the fluid level and top it off before your Mom goes shopping--this has saved me lots of cash over the years--good luck.

An old friend in military maintenance said they used to do this like the aboved mentioned, except they would put fresh fluid into one bucket with a mark at X amount of fluid and make a mark on another empty bucket at the same heigth, the tranny pressure line in the empty bucket and the return line stuck in the bucket of fresh stuff that way it would replace what it put out by itself with no monitoring so to speak. After X amount of fluids were sucked through they'd reinstall the lines and check tranny level and top off accordingly.

Well that makes sense--I guess you could find the total volume of your tranny and do that. I was in the mechanized infantry long, long ago and the armored personnel carriers had small block Chevy's with automatics, very well maintained.