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!
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