Gaining

My girlfriend has been looking at gaining in as healthy a way as possible, any tips? Particularly around how best to gain while still exercising regularly. At the moment she's been using gainer shakes, serious mass, but just doing light resistance training twice a week. She's not a big eater and wants to avoid cholesterol so the shakes seemed a good way to boost calories while keeping an otherwise clean diet. Any experiences with this kind of gaining plan? I do love the idea of her being a little chubbier everytime we go do our training together. 🤭