I'm researching a few things for my timeline, and as a result I've been juggling a few POD's in respect to South America. One of these is the medium/long-term survival of the Empire of Brazil under Pedro II's daughter, Isabel. Thing is, I don't know when is the best time for her to replace her father (say, he retired or died), especially with the 1870's and 1880's being a somewhat fuzzy decade(s) to me.
So, when is the best time for there being a somewhat smooth transition of power between Pedro and Isabel?