1999 Cadillac Deville to substantiate what the dealership m

Other Category problem
1999 Cadillac Deville Engine Size unknown Wheel Drive Type unknown Automatic 90,000 miles

My mother has a 1999 Cadillac Deville. She recently took it to the dealership service department (as she does right on shedule for all maintenance and repairs) and they told her she had a radiator leak and water pump leak. The cost to repair quote is $1200. Additionally, they told her that if she spends that $1200, to be warned that in this make, year and model, they fear she will be soon replacing a leaking/blown head gasket, which will cost her $3600. So, they recommended she might want to consider buying a new car soon. My mother is an active 77 year old, but knows nothing of cars. I know she has paid a fortune to the dealership over the years, but this seems like they are trying to get her to buy a new car. Can you please tell me what these repairs would cost, both at another dealership or a private shop and if they are repairs worth making for this car to last for several more years?
Thank you,
Jayne