Thank you for your query.
Is your daughter receiving any other medicine apart from Advent? Decongestant/cough
syrup medicines do make a child drowsy.
As regards giving Advent for one more day I would stop it in case you have to purchase another bottle. Since she has already received 5 days of medicine and is much better according to you then it can be stopped. If some dose is left over in the earlier bottle then do continue it for another day.
I hope I have answered your query to your satisfaction.