Hi Garethusa
I recently raised a batch of Bettas through childhood, and sold the survivors to the lfs when they were 5 months old. I say survivors because the spawn was plagued by intestinal parasites. For weeks I didnt know what was wrong, and treated them for everything in turn, everything except higher parasites. So, each day maybe 1 or 2 babies would exhibit stringy white poos and die soon after (the parasite looking to move host as the current host is in bad health and not providing it with food). It always seemed to happen to the smallest of the fish in turn. After biting the bullet and adding the anti-parasite stuff in frustration (the product warns against using it unless absolutely necessary, and knocks out the filter completely, and turns into chlorine gas if the pH drops below 6.5 etc etc) I knocked the parasite plague out. In hindsight - all of the fish had intestinal parasites, -only the smallest in the tank at any one time succumbed to it because of 'underdog stress' if you like. Eventually all the fish were going to die (I lost over 1/2 the spawn). Upon adding the meds, EVERY fish had stringy white poos - dead parasites, and were all great the next day on. So, its possible all of your fish have these intestinal parasites if Violet did, but they are healthy enough to survive with them. If there was a med available to you to treat your remaining fish as a precautionary measure (thats not a dangerous one like the Interpet one I used) I would go for it.
If your fish are really fine I wouldnt risk it, maybe most fish have them but remain healthy. I once treated my breeding stock (2 males and 9 females, divided) tank for intestinal parasites as they had the stringy white ones, the pH dropped the next day and they all died before I got home from work.
Sorry for all the waffle, I just hope my experiences help you, and your fish remain well
Lee