What Causes Anxiety And Depression In Young Adults?

My 27 year old daughter was prescribed escitalopram for anxiety and very mid depression. She started out on 5mg per day for one week. She had some side effects but not too bad. Then she started taking 10 mg, and she had a decrease in appetite, dry mouth and ver mild fatigue along with an increase in anxiety. After a week those side effects went away. She started feel better overall, but 3 weeks later she got an upper respiratory infection. At first we thought the fatigue she was experiencing was due to the virus, but it has been a little over 2 weeks now and the fatigue has gotten worse and she has slight nausea and slight dry mouth, but her congestion is almost gone. My question is- is it possible for her to get side effects again (having no increase in dosage) after having no side effects for 3 weeks? She has been on the 10 mg dosage for 6 weeks now