My 12 year old daughter said she feels discomfort when breathing. she said that it feels like there's a lump in her throat..

Need details: Is her breathing compromised? If you feel that it is, then you should probably have her seen by a physician as soon as possible (like, now) in order to protect her airway. Any fever? Other potential causes include asthma, foreign body, Ludwig angina, vocal cord dysfunction (less likely)

Needs evaluation: possibility of anxiety is there but other causes like undiagnosed asthma needs to be considered. Evaluation by pediatrician is recommend