My dog is uncomfortable doing a trick?

I am trying to teach my westie to roll over and when she lays down I try to scoot her over. I'm not being aggressive or anything. She lays down sometimes on her side, so i try to turn her over and say roll over. One time she did it but she "spazzes" out and just jerks over. She knows how to lay down on command. Also when I try to pick her up, she doesn't feel comfortable and I actually have a scar from her nails scratching me. I try to pick her up by taking her paws and putting them on my shoulders and I lift her bottom and hold it up. Is there a reason why she doesn't feel comfortable? I mean all of my friend's light dogs I can pick up while they're sleeping and they stay asleep. Thanks! Sorry this was so long. :)