Stressed Hermie?

Question
Hello, I believe one of my hermit crabs is stressed, though I do not know why.
She molted around a few weeks ago and she seemed okay, active and her molt went fine.  Then, one of my other crabs died for no reason. I examined my entire tank and could find nothing wrong.  I decided he was stressed from bullying.
After that, I am not sure, but have a vague impression that the crab of concern is either stressed or depressed.
Comparing her to my other crabs, her antennae are not as active, but they do move a bit.  
I recently hand fed her and she seemed eager to eat.
But she does not move around while in the tank.  She just sits in one spot, though she will come out when I lift her up.  If I put her down, she does not seem to want to move around at all.
She is a purple pincher and I am concerned that she may die, though all my other crabs seem to be fine.

TANK INFO:

Humidity: 70-80
Temperature: 72-82
Substrate: Play Sand (I baked it before adding it in), deep enough for all crabs to molt
Water: De-chlorinated water and salt water
Tank: 10 gallon glass aquarium
Crab Count: 5 crabs, smallish-medium and one medium
Food: Fresh fruit and veggies, all organic, no commercial food, fed everyday
Hiding Places/Decor: I have a artificial vine, a plastic toy play thing, two huts made from clay, two cork wood logs, and a coconut climbing mat.
Shells: I have shells of various shapes and sizes, around 3 for each crab. They have been boiled and cleaned.  

I believe that is all, if you need more information, I would gladly give it.
Please, do you think my crab is stressed, sick, or normal.
And if you believe she is stressed or sick, do you know what I could do for her?

Also, since I do have a larger crab, maybe 2 or 3 times her size, do you think she could be a victim of bullying?

Please, I would like to know your opinion.  Thank you so much.

Answer
Thank you for all the extra info, it really makes my job easier.

Now, how new is this particular crab? It sounds to me like he/she might be pre-molt. Has the crabs exoskeleton or eyes changed at all lately?

Bullying is unlikely, esp. due to size issues. Unless you see aggression more serious than antennae fights, I wouldn't worry about that.