I never had much luck with sealers.Most are about useless with any antifreeze.
I had no luck at all with repairing one.If like newer radiators, they would be plastic.
Have her turn the heater off, so no more fluid runs thru it.
Once the coolant runs thru it and it leaks thru the heater ducts and defroster ducts,it's hell getting it out of there.
Can't dad lend her the money for a new core?
Probably getting it out/in in will cost more in labor than the new core.
See if Rockauto.com has one. They usually have the best prices on auto/truck parts
