What could’ve possibly made my calathea to start dying?

1st and 2nd pic depicts my calathea in the present day. The last are how my calathea was this summer.

I only water with distilled water and kept her in the same place till now (but there is one exception)

Now, the exception: i had a friend help me water my plants while I was away in august and even though I explicitly told him to use my distilled water, he absolutely ignored me. Plus, he moved her from her spot to a more sunny one (by accident) and it stayed there for two weeks.

Was it that great of a shock that even now, neary 3 months later, it's this bad?