Wow. She is tiny!

Poor thing.
I have 4 females born in November. So that makes them about the same age as your girl. They were about the same starting size too. The largest(youngest) one is currently ~500 g. The smallest one(oldest and a slow starter) is close to ~300.
The average growth of the whole lot is a little less than 100g a month just to give you a comparison.
Something is definitely not right. I hope the most your girl has is parasites. Those are easy to get rid of compared to other potential problems.
Ask your vet if there is an option of a cloaca wash to get a fecal sample. It can be a little stressful on the snake, but it will speed some tests up as it might take weeks for her to defecate on her own.
And a full panel just means a whole range of tests from a sample.
As for tank screen top and humidity, there are few options. You can use a larger water bowl and leave it in the hot side of the tank. You can cover 90% of the screen with tin foil, plexiglass, or a damp towel.
Keep us posted!
And thanks for sticking around and giving this forum another chance.
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