Hi there!
I believe that one of the causes of your Sundew's death is because of the plastic structure you put over it.
Sundew plants need humidity, yes, but not too much. The average humidity of the household should be enough. Too much, and you'll be harming your Sundew plant.
You should remove the plastic structure. It is acting like a terrarium, and terrariums are bad for most carnivorous plants.
Please make sure that your Sundew plant is in an environment of around 55-85 degrees Fahrenheit. It is the ideal temperature for producing dew.
Make sure as well that the Sundew plant is receiving plenty of sunlight. They enjoy bright, slightly filtered sunlight for around 4-6 hours a day. If you don't get much sunlight near your area, it's best to buy a light to compensate. Fluorescent light bulbs and the ones used for plants are best.
Necessities for Sundew plants:
1. It kind of looks like you put your Sundew Plant in just regular soil. Don't use MiracleGro or whatever. They'll kill your plants. Carnivorous plants prefer the long fiber sphagnum moss. A seller I recommend to buy the pot and mix from is Joel's Carnivorous Plants. They have great customer service and usually give more than what you paid for. He specializes in Carnivorous Plants.
2. Don't use fertilizer on your plant. Carnivorous plants have roots that aren't meant to really suck in anything, such as minerals. They are just meant to anchor the plant in place. This is why you also don't use normal tap water.
3. Use distilled water. This water is very pure, with no minerals in it to kill the plants. This is ideal for your plant, and the bottom of the roots (I believe the yellowish parts) should always be at the top of the water level. They need to be submerged not above, and not below that level, because then it will either not get water, or the roots will rot.
4. Don't swarm it with bugs. It is a plant, after all, and can perform photosynthesis. Too much and you'll be killing the Sundew plant.
Good luck, and happy growing!
