I have never experienced a game-stopping glitch or a progression blocker in a Nancy Drew game, have never had to start over, and have played every one of them multiple times. I would say that the best help you are likely to find would be to do a search for your problem on the Her Interactive message board. There are people who post there who have played these games even more than I have, and it seems likely that you might come across an answer to your question there.
I am not saying it isn't possible to have an issue like this with an ND game, though. But of all the old adventure games I have played, this series in my experience is one of the least likely for this to occur. I would never have played them as much as I have if this were not the case, as I hate that sort of thing in an adventure game. I do hope that you haven't been this unlucky.
NDLVR, a GameBoomers member, seems to have a lot of saved games for the Nancy Drew series. I know of a site that has some but unfortunately none for Alibi in Ashes. Perhaps she could help you out. Maybe she will see this thread.