I understand that you want to have live plants but if I were you I’d remove at least half the substrate or replace it all together with repti bark or cypress mulch or something comparable. A couple of inches of substrate and some fake plants with the other accessories that you already have and you have solved your heating problem.
But then again I’m a tub keeper so what do I know! 
I appreciate the insight for heating thank you! I’ve looked into a both types but wasn’t sure which to go for so this helps a lot. I’ll probably get a CHE for her to help overall temp and have it a little warmer on one side so she still has a cool spot. I really appreciate all the insight and hopefully I can get her enclosure to a better spot and she’s happier in it. I have the Zoo Med Repti-Temp Digital Thermostat as well as a thermometer that sticks to the side of the class that measures humidity and temp.
Opps. I see the thermometer vs stat was answered!
Late to the party 
Anyway…The thermostat probe should be between the heat pad and the enclosure’s bottom. It’s important because an unregulated heat pad can get to temps as high as 140 if left alone. 
The thick soil may be keeping the heat down and the warmest safe spot She can find is the spot under the dish. Definitely wouldn’t want her borrowing down to deep to a hot hot pad tho
Sounds like a good plan!
Looking closer at your setup, I have a couple additional suggestions.
First is that I’d recommend covering a portion of the top screen with heat-resistant foil tape (only put the tape on the outside top of the screen, never put tape inside the enclosure) and ditching the towels. With a CHE up there on top of the screen, those towels could pose a fire hazard. That CHE housing can get quite hot. The tape will serve the same function as the towels in terms of helping retain humidity, but without the fire hazard.
Second is that I recommend you get a better thermometer/hygrometer. Those analog ones that stick to the side of the tank just aren’t very accurate. I have one of these, it works well and is quite accurate: https://www.chewy.com/zoo-med-digital-combo-reptile/dp/257703 Or if you want something more high tech, I also like these: Amazon.com
It’s also a good idea to have an infrared temp gun, as that allows you to instantly temp check various spots all over the enclosure. This is the one I have: Amazon.com
It’s really important to ensure that you’re working with accurate equipment and readings when you’re setting up a new heating element. I also strongly recommend that you remove your snake from the enclosure while you’re getting the new heat source dialed in. It usually takes a little trial and error to get the heat source and thermostat probe and thermostat settings just right, and you don’t want your snake in there when the inevitable errors occur.