if you’re not feeling hungry, it’s easier (in my experiences at least) to drink something. a protein shake is good! smoothies are also good, but i would suggest putting in a protein element to get you the stuff you need. and honestly, sometimes, you gotta force yourself to eat. small snacks throughout the day can help, especially if you’re not up to eating full meals ^^
is she a grazer? a lot of my friends have issues eating proper meals but have no problems with snacking throughout the day. ive also had appetite issues and sometimes have managed to eat things that look good as a snack but are actually pretty filling/healthy (onigiri and any rice cake/glutinous rice ball variants worked well for me personally)