Welcome to the forum, and sorry for your loss.
The main value will be sentimental. Certina are good quality swiss watches but servicing movements is expensive and this watch has little monetary value for the following two reasons:
1/ it’s gold plated -as evidenced by the steel back, and the lugs are scratched even though the dial is very clean.
2/ While Certina was a good quality brand, and good value again in terms of quality, it is relatively obscure brand nowadays.
I would say it’s worth about 150 euros- which means the cost of a service in most countries of the western world unfortunately exceeds the monetary value of the watch.
That being said, it is a clean and elegant 1960s watch- and if it comes from someone you loved it is entirely worth servicing and wearing as a precious keepsake.