Chis shake, period. Both mine shake when they're cold. But they also shake when they're happy, nervous, excited, worried, expectant.......you get the idea.
So the shaking isn't any indication that she's cold. What you can do is get a fluffy, fleecy, stretchy sock, (the kind I wear to bed when it's cold) and cut a hole for the head and a couple for the front legs. It won't be pretty, but it will keep her toasty warm till she grows enough that regular dog clothes will fit better.