I can't recommend an appetite stimulant per se. But I know I used to really force myself to eat because I needed to eat and was about ready to faint from low blood sugar, not because I had any appetite. As I have gotten healthier, that changed. In recent months, I am beginning to really enjoy food in a way that I never did before. It's not any one thing I have done. I did lots of things to get here. Some that I think are the most directly relevant to your question: I did things to help heal my gut and get off digestive enzymes and that helped me stop dreading eating and made it less of a chore to eat. And I got my excess acidity under control and that meant I had a lot less stomach upset. Etc.
Some things I would recommend starting with: Coconut oil and sea salt, plus either: glyconutrients (ideally) or aloe vera supplements and combining healthy carbs with sea salt and healthy fats. (I have some remarks on that here:
<a target=_blank class=ftalternatingbarlinklarge href="http://www.healthgazelle.org/combiningseasaltcarbsandhealthyfats.shtml">http://www.healthgazelle.org/c...bsandhealthyfats.shtml</a>
Glyconutrients are pricey, but sea salt and coconut oil are some of the more affordable things I do and they both help me in so many ways. I would start with ONE thing at a time though, so you have some idea what effect each one has, and wait a week or two before adding the next thing. However, for me, combining these three things had a multiplier effect on what this did for me. It wasn't just like adding together the benefits. It went way beyond that. I would also start slow and ramp up gradually to see how she tolerates stuff. All of these things can promote diarrhea as they help the body heal and move crud out the system. Taking a high dose can cause really severe diarrhea, which can be a very negative experience. Though, for me, the diarrhea from taking supplements and gradually healing is nowhere near as miserable as the diarrhea from antibiotics and illness. It's mostly inconvenient (due to having to dash for the toilet and sit there a long time). I have learned to take extra supplements evenings and weekends, where it doesn't really matter if I have to do that.
Good luck with this.