She's really mad at you now. Why don't you give her some time to cool off/down and call her later?

What's the difference between cool down and cool off?
Cool off = become calmer
Cool down = allow the body to return to its normal temperature.

In your sentence, either might be used, as the second idiom can be used as a metaphor for allowing the temper to cool down.
Thanks Feebs, so Cool off is equal to CALM down?