A picture would be really helpful but there are several things that may be going wrong. In no particular order .... Firstly, leggy plants are telling you they need more light. Not necessarily direct sun but bright light. Secondly, peat moss isn't a good mix for a house plant. If you can't or don't want to make up your own get something labelled as being specifically for houseplants. Thirdly, watering is crucial and overwatering is the number one reason for houseplants failing. Lastly, pinching back will only promote growth in a healthy plant which has the energy and root system to recover. Pinching a sick plant doesn't help. By removing those last two leaves your plant now has no means of photosynthesising apart from a little chlorophyll in the stems.

Without a photo all this is conjecture....

Lack of light. Plants with coloured/variegated leaves need light to maintain growth.

"No plant could be happy for long in pure peat, or any mix with mostly peat."

No, Venus Fly Traps do well in pure peat moss. And, almost every plant does well in 2/3 peat moss plus 1/3 Parboiled Rice Hulls (PBH). "2/3" is greater than half which is "mostly".

I've not heard of using peat and parboiled rice hulls, but I do know the "Pink Polka Dot" plants are humidity lovers. I've never had much luck with them because I live in the high desert, with often single digit humidity readings, so I take care to buy plants that can handle lower humidity. You really do have to put thought into what types of plants will do best in your situation. Do you have air conditioning on? This can also really dry out the air. Is your plant on a pebble tray? That will help with humidity. So will misting once or twice a day. The misting only has a brief effect, but it makes me feel like I'm doing something for my plants! I agree about the peat. I'd buy a good potting soil (not moisture retentive) and mix it with nearly half perlite. I agree that you need to post a picture.

Are these plants in the family as the fittonia (nerve plant)? If so, they loooove humidity. I was never able to keep my fittonia from wilting even in the humid south. The pebble tray might be a good idea, along with better light and a soil mix as others have suggested. If it recovers you might think about putting it in a terrarium to give it adequate humidity. There are lots of ideas on the web featuring this plant and fittonias in terrariums.