My idea is that they know better than we do about what temperature their body needs to be at any given time. As long as you're satisfied that you are providing her with a proper range of temperatures, which you seem to be, then let her do her thing and try not to worry about it. It's certainly good to take note of, but not something to worry about.

In her defense, "cold to the touch" doesn't mean a heck of a lot. Our own hands vary between 86°F - 96°F based on a number of factors. Being that they're cold blooded, they will feel "cold to the touch" to us a fair amount of the time being that we're providing them with a hot spot in the 90°F range.