holding your finger in her mouth is like a ratty handshake, or is a way to say "hey! look at me! me! over here!" i have a rat that will hold my finger every time i put my hand in the cage and i've had babies that would pull my hand all the way into the cage and away from the other rats at the door. in either case its a way to get attention from you and show their love.
the lazy eyed thing is her saying "ooooh, yeah, right there. mmmmm, feels goood...". all rats will do it if you find the right spot regardless of their color, coat, eye or ear variety.
sounds like you have quite the sweetheart on your hands, congradulations!
You would know if she was tense. She would have her legs spread out almost, her tail stiff and her ears perked high up. She would also feel tense. Sounds like she's just loving the petting. She probably will get used to being picked up in time, if you work on it everyday. I have a rat that hates being picked up, I think all of them don't really enjoy the process of being picked up but once they get in my arms they feel safe and are good to go lol.