Yeah, that second plant looks really sick. Looks like it already had the problem starting from day one. Due to the white spots I would consider thrips, leaf miners or genetic defect. Does not look like powdery mildew to me. Not to dampen your mood, but I think she'll die in the next 2-3 week :(
Definitely keep both of the plants distant to each other. With damage like this, you can't know if its a virus, genetics, insects or just the dog hhaha.
But still, happy growing!
@Herikus, yes, she had that problem from the very beginning, and now I don't really know what to do. Maybe it's a good idea to put it somewhere far from others