I used to put the heater in Zander's room before he went to bed so he didn't go into a cold room & then turned it off. If he woke overnight the heater would go back on while I was feeding & settling him & then it would be back off again.

Check the back of her neck, just below the hairline & see if it's warm or not. If it's warm, then she is warm enough & doesn't need anything else. If it's cool then she needs to be warmed up. Don't check for warmth in her hands or feet, bubs extremities tend to be cool.