We just came back from a week long vacation to find her like this. I believe these leaves were the new ones she was pushing out before we left, however the 4th newer one looks undamaged so far. She is currently pushing out two more leaves.
Everyone else, including the Rattlesnake plant adjacent to her are fine. She's the only one with damage.
The windows were covered and it's possible the temp got a little low (63 when we arrived). My main concern is I had to have my humidifier off all week. Usually it's on for 12-15hrs a day.
I live in the Midwest and use hard/iron rich tap water over winter months. Rainwater during the spring/summer. I put out a bucket to catch some water during today's storms I can use later this week.
The last two pictures are an attempt to show possible light. We had storms while we were away so it's possible she was in quite a bit of darkness. Typically I have the grow light on, but I wasn't able to use that either while we were gone.
I want to make sure I'm diagnosing her properly before doing anything. I assumed low humidity, but these kind of look like burn type marks which has me questioning the cause. I know the soil looks kind of dark in the pictures and the perlite is orange (due to iron not mold), but the top is dry and doesn't stick to my fingers.
I almost killed her back in December trying to get rid of what I thought might have been a small spider mite infestation (burned her leaves with the wrong solution of hydrogen peroxide to water and her leaves did something similar then), but she bounced back beautifully until now.