Wow hold on there
Spring water isn't the best... Sometimes people have to use half tap wate and half spring water because something in their water is too high. However, spring water needs to have suppliments for the stuff taken out. I know very little on this, but someone else might chime in.
As for the lily, did it cover the WHOLE surface? If it did she could've found it hard to find an opening to breathe.
The bowl is FINE!!! Don't need to defend yourself at all! How big is the bowl?16 cups per gallon. You can measure it that way.
How often did you clean it?
Did she show any other signs of illness? were her fins stuck together? was she really pale with stress lines?
Andlastly, sometimes bettas just come sick.