If it's her first trimester, she actually probably doesn't need any more calories than usual. You do up it for the second and third trimester but your body WILL tell you that.  Mine made me RAVENOUS all the time, but I still prepared myself normal portions and was satisfied once I ate them. Sometimes I'd eat a normal portion and my body would say, "Nope, still hungry" and I'd eat a little more. Fats take these hunger cues to mean, "I should eat an entire cheesecake without stopping" or "I need two combos at McDonalds" rather than just eating like normal to satisfy their hunger. Same thing with breastfeeding. During breastfeeding I was starving all the time, and my body usually told me I wanted more food once I ate, and no matter how much I ate, I burned all the calories between my normal activity, exercise, and breastfeeding.