I think you are getting quite close.
Just a remark, related to what
Nerwen suggested (and what
Pitch mentioned too, only I didn't realise he might have meant it that way), if you are trying to make some timeframe out of what is said, the riddle is
not supposed to mean that the path of the mother ended by the western shores between the time when the mountains shook and after the darkness came, there suddenly was another path appearning or anything like that. It was simply (perhaps in somewhat confusing way, I apologise) meant to say that the time when her path came to end by western shores is defined by two things: it was after the mountains shook, and before the darkness came; they are two descriptions of the same period. Sometime in this period, it came to be that the mother's path ended by the western shores, as in, a finished process (not like that it ended somewhere between these times and later it suddenly ended elsewhere - that even wouldn't make sense, especially if we take the mother literally). Hope it is clear what I mean...
