I have two rats, one is extremely skidish

Question
Hello,
two months ago I purchased two baby female rats from a pet store. One is a hooded dumbo, the other an albino (who had a brown backside as a baby and now is completely white, weird). I have owned rats before, so I trained the two of them and socialized them like normal. They get along great, and the dumbo hooded has become completely attached to me, is totally friendly and playful, and very smart and curious. The albino however, is extremely skidish and it has been very reluctant to get out in the open. She takes treats from my hand, and she knows her name, and she doesn't mind being petted, but she does not enjoy being picked up. Neither of them would ever bite, but the albino will not run around and play like the dumbo, and she will only come to you after a long while, but won't stay out for more than a second. If she is given free roam, she hides all the time, in one of their favorite nooks, while the other comes out to play and investigate and have fun. She isn't scared of me it doesn't seem, she's just scared. I'm now thinking that she might have been in the feeder bin, or even put near a predator in the pet store, or something but I have no idea. It has been two months, what do you think I should do?

Answer
So sorry for the delay. I have been on vacation.  

About your scared little rat....what is the play area like? Tell me everything about it such as where it is, what you have in it, what is the level of noise and what noises are there, do you have any other pets such as cats? If so, do they come near the rats cage ever?  How long do they stay out for play time, how often do you take them out?   I have one rat that wont come out of the cage unless I lean forward and let him run down inside my shirt and I take him out that way. LOL.  He stays in my shirt and here I am, leaning forward so he isnt smooshed by me...LOL..and he comes out after a few minutes and runs to a safe secure place as well, but he eventually comes out of the little hide out and follows his brothers around. One wrong sound from outside the room sends him running back to the cage but he comes out again (this time he doesnt need to use me as a vessel to transfer him out) and this goes on for at least 20 minutes till he feels safe.  I have had these three boys since they were three weeks old, just got them in June of this year from a very good breeder, but he was the runt of the litter and although he is now the largest of the three, he is still skiddish despite being properly socialized as a little pup.  It doesnt always matter how much they were handled, sometimes they are too smart for their own good and fear the worst case scenerio until they are sure they are going to be OK.