no, the only person I think looks like Thelma Lou is Sharon deSpain...
I believe the actress your thinking of is Barbara Perry...
you're right. Now that you mention it Sharon DeSpain did look a lot like Thelma Lou.
I also think it's funny in the second reunion episode when Aunt Bee is looking over the names of the guests she reads "Sharon DeSpain" and says she remembers that name. Andy quickly says "we were in Civics Club together".
btw, Sharon deSpain was played by Peggy McCay
Lydia Crosswathe was sitting in the diner at a table with a white-haired man who could be her father in Earnest T. Joins The Army. It was when Barney ordered breakfast at the counter and then asked the fella next to him; who was reading the paper, to pass the sugar. It was Earnest T. and Barney arrested him.
In episode 1 the new house keeper, when Aunt Bee first comes into the house, there is a picture of a woman on the wall in the living room; must be Andy's wife.
I heard this a a picture of Frances Bavier in her broadway days. It is in other episodes hanging in different places too.
You can also notice in that first episode or maybe more eps, that the whole front-door side of the living room is raised about six inches on a platform about four feet wide. Probly part of the removable set. I imagine they could grab whole sections of the set and just pull it out and move it around. That might explain why the kitchen door is moved in the color shows. They probly used that stage for another show or something and then put it back together wrong as a simple human error. There's a scene I watched today showing Roger Hanover and Aunt Bee in the kitchen and its shot from 'behind' the kitchen sink. BTW that Roger, I can't stand him.
There are a couple of scenes where the camera is behind the kitchen range also, as if it is pulled out from the way a good ways. I think one is the very first episode where Opie is boiling 45 minute eggs.