Carnivorous Plants/Browning stems of leaves
I purchased my Venus flytrap a month and a half ago as a tiny little thing. I repotted it, gave it as much light as possible, always kept the dirt saturated. After reading, i learned that warm, humid environments are it's best bet. So I went out and bought a plant desk lamp and make sure she gets 12 hours of that. Then, I purchased a BioBubble Terrarium. Two nights ago I repotted it in the terrarium, watered it fully (maybe even in excess to saturate) and also placed old fish bowl stones that had previously been cleaned in the bottom for draining so the roots don't grow fungus. We were going out for the day today (two days after the repotting) so we decided to take the biobubble outside so it could get a full 12 hours of real sunlight. Well when we came home 6 hours later, the leaves were browning and I noticed it still had the dirt trapped from the repotting, and they aren't opening. I have done my homework and am now kicking myself for why it's dying! Is it in shock? And since most already have a brown spot or two is it basically done for? How can I help it?
It is true that Venus Flytraps live in bogs and typically have a humid environment, however; they can adapt to low humidity environments quite well and grow best open pot.
They are full sun plants, requiring as much sun as a typical garden plant outside gets.
The problem you are running into is that you placed it inside an enclosed terrarium and then placed it in full sun (this is one of the main reasons why people accidentally kill Venus Flytraps), which basically is like placing it a slow cooker (it likely held in excessive heat). This is one of the main reasons why terrariums are a bad idea in general for many carnivorous plants. They can work, but require so much more effort to maintain.
Venus Flytrap basics:
Use any neutral pot made of plastic, wood or ceramic and do not place a cover over it. You would only need to worry about humidity if the plant came from a high humidity area and your concerned about placing it in a drastically lower humidity area. You can remove the dome now since the plant has not had time to adapt fully to high humidity.
Use mineral free water like reverse osmosis, distilled, or rain water. Water with high levels of mineral deposits and nitrogen will cause a change in the Ph level of the acid soil the plant lives in and kill it.
High light levels. You are correct that this plant requires full sun. If you grow the plant indoors, this is difficult to obtain since windows only provide a sliver of light for a few hours a day and the light is usually filtered through the glass, so only a fraction of the suns intensity is getting through. I do grow my Venus Flytraps indoors, however; I have them under 36,000 lumens of florescent lights, equating to 12 tubes of 40 watt cool white T-12 tubes (yes, the 4 foot long shop light tubes). This would be a bare minimum for light capable of allowing for the plants to thrive (full sun provides between 25,000 to over 50,000 lumens on the planet surface). If outside, place the plant in an area where it can receive full sun for most of the day and ensure it is not covered with humidity domes.
Your best bet for now is to remove the dome, clip off any dead or dying leaves, leaving anything green for photosynthesis, keep the plant in a sunny area, keep it hydrated to where the soil is just moist all the time (also easier with a pot with drain holes), and last but not least, leave the plant alone for a while. Movement and change affect plants and stress them more so than Humans as plants are meant to be rooted to one spot. I have seen plenty of people move their plants from room to room and inside to outside in a daily cycle which eventually sickens and kills plants due to humidity, temperature and other environmental changes that occur too quickly for the plants to keep track of. The last thing this plant needs is to be repotted and moved about too much. Set up the environment and then leave it there.
Only time will tell if the plant will survive, however; this is part of the learning process. I have killed plenty of carnivorous plants in my time as I was first learning how to grow them. Now, it actually feels difficult to kill them. That feeling will begin only after you have obtained experience. Don't give up and take each step as a learning experience and try over and over until you have the right set of conditions, experience and knowledge.