Clear string on guppy? Help?

I had the same problem, but Im guessing your guppy might of just released her babies. Try looking around the tank in the decor you have setup (if you do) if not that guppy might be sick. Keep an eye out for any signs of illness. Its good you separated it from the others. If you don't see any results of anything put her back into the tank again. Hope this helps ;)