Please go to the vet. I don't know where you heard they'd had contractions for days before birthing, but usually a chinchilla has a pretty smooth and easy birth over with within a couple hours or so.
Are you sure you feel movement in there? I would just be frightened if one is stuck in the birth canal, that the others are stuck behind and will die.
I'm not sure where you got your info on about spotting and such, usually it just happens and it is maybe an hour - four hours(for multiple births and placentas and if a baby should be breech or stuck - it can take a little bit more time than a usual birth, and can be up to four hours, with help from you or your vet to maneuver a breech baby out or a stuck kit...).
There's never really a lot of blood with the birthing, not quite like human birthing. Please get her looked at by a vet if you can, to ensure no babies are stuck in the birth canal.
Sometimes females stop contractions because the kits are stuck in the birth canal. They need a shot of oxytocin to help get the contractions going again. If that does not work - if the baby is too big or the birth canal too small, you may have to look at other alternatives or else you will lose both mom and her babies. Good luck and hope she is all right!