What to do if you know your guinea pig is dying?

Hello, my 3-year-old guinea pig was and is sick. We went to the vet and got medication, but when we went back to the vet, they said she would probably die in a few days/weeks. I don't know whether I should pet her now before she dies, or whether I can still do something good for her and myself mentally. I want to prepare myself so I don't have a complete breakdown. But I don't know how to prepare. Do you have any tips?