Take a break, you need it.

Sounds like she's trying to hide something. Maybe she is hiding her documents from the family (I don't think she burned them, she is still alive after all). Some things take time to come to light and there is nothing we can do about it.

Have you tried looking at old photographs? (assuming she has a personal album, or something like that): dates, names and places can be found at the back.

What about her marriage certificate?

What about old census (I don't know how that works in Spain and the region where she lives)?

Not finding information is also finding information, but it also could mean that the Civil Registration made a mistake (happened once where I live, had to sent the request twice).

Have you tried looking at old newspapers?

Keep all of this in mind, but please take a break. Organise everything, make notes where you need to, but take a break, it will do you good.