I see no need for her to have died at 17 years of age. One of the more ineresting things about Lolita is that it is Humbert's words, as if it was told to Nabokov who then put it together. We readers don't get anything else, and there are goo reasons for believing that lage parts of Humbert's narrative is composed of lies. There is nothing between the covers of that book that can be accepted, including the Introduction and the author's Afterword.
The Introduction is perhaps more fictional than the rest, because it purports to be the truth about what happened in the end to the characters. As a carefully xynical reader, I see no reason to accept any of it. There is no reason for Humbert to have been arrested, unless Dolores accused him, so there was no reason for him to have been in jail. With that thrown out, there is no reason to think that he died in jail, because he wasn't there. Have you read The Great Impostiror seen the movie? The character did exist, but he disappeared shortly after being interviewed. The author investigated the claims and included those that could be backed up. I regard Humbert as a similar sort of characterBut while he done criminal acts, there was no way to connect him without Dolores' testimony.
I'm not going to write the whole thing here, but I think that you should get the idea.