LOL--Straightening out a snake to measure it is near enough to impossible to just call it that!
Just get a piece of string, lay it along her body until you get to one end, pinch that spot (of the string, not the snake), & measure the string.
However, with just what you've given us so far, it sounds as if one possibility is that she's becoming fertile & so isn't quite as interested in food, though that's going to depend to some degree on her weight.
You also need to increase your temperature range a bit--80 deg on the cool side to up to 95 deg on the hot side. You can let the 80 deg ambient temp drop to 78 at night.
What humidity are you maintaining?
Finally, she just may have gone out of a growth spurt, so her body may have plateaued temporarily as it "rests" before beginning another growth spurt. Most animals don't grow at a constant rate.