hello,
welcome to healthcare magic,
As your daughter is 18 year old , she falls in the teenage group. they have their own idea.
regarding your concern of not eating properly related with any psychological or habitual thing. but in certain diseased condition also appetite will not be there like
anemia etc.
if your daughter is healthy ,active and she didn't complaint of any problem related with her physical and mental health and you didn't find anything abnormal ,(.faitgue,loss of weight )like that then no need to worry about her appetite.
you need to advise her to take food in proper time.
it is not advisable to give medicine to increase appetite. If she takes proper food in proper time and she is energetic and active.
taking Vegetable soup,nuts like almond,channa,soya ,pea nuts and diary products,urad dal preparations will be healthy for your daughter at this age.
Hope i answered your query.
Thank you