I would either:
Take up boiled (still warm/hot) water in a bottle warmer and then add the formula if and when she woke up
or
Use cartons at night, heat it up before bedtime, store in a bottle warmer thing and give it to her whenever she woke.
You can also get those portable bottle warmers from asda dirt cheap. Could then have it all ready, press GO if and when she woke up and feed her that way.
Sawyer has started waking up more often now too. I think he's just a week younger than D x