The biggest issue would be rodent damage. You'd be surprised what can be done to save old paint. That car doesn't look bad at all in the pictures. If it was my car I'd keep it regardless. She's had it this long and the value just keeps going up on original unmolested cars. The big money would be the paint. The interior would be next in expense. Dirty things can be cleaned though...and plastics can be painted.
I mention rodents because I had a barn find car that was beautiful after a good cleaning and a buff job. The problem was that they got into the wiring under the hood, behind the dash, and even in the trunk. They caused a constant chase of electrical problems. Mice will chew on the weirdest stuff. They caused more damage and caused me more headache than it was worth. That car was a 84 SAAB 900 Turbo and didn't hold much value from the start.
That car is a GT convertible and will have lots of value. A situation like this depends on what she wants. To make it a reliable driver could be cheap... to make it like new ( new is not show quality) will take 15 to 25k going through the engine parts, transmission service, interior, suspension, electrical, top, and mid grade paint...or paint correction. For a show quality car it would be north of 25k....money would have to be a non concern. It looks like a great candidate for restoration or making a good driver.