The best thing to do is review deaths in Caracas in the time bracket you have. Check FamilySearch.org
I am currently indexing all births in the State of Miranda for 1875-1879 or so. I have not seen many Rivas in that time frame. But once you find her death cert - it will list her age and likely her birth place. I hope this helps. Venezuelan genealogy has not caught on popularity (yet). Hang in there and keep searching and indexing on familysearch.org and it will eventually be fruitful for you.