Electronic blankets should not be used by patients with diabetes. However, an electric blanket can be used to warm up the bed before bedtime, but it should be removed before climbing in. They should not use this blanket because of insensitivity to heat.
The electric blanket is safe to warm the bed, but unplug it before she gets in the bed. Keeping the room a bit warmer will be helpful in making the transition. The risk of a serious burn is low, so perhaps you should not hassle her. Neil