My 13 year old starts choking everytime she eats. what should i do? is this serious? she has minimised her eating because of this and i'm afraid she will become underweight?

Suggest you have her throat examined by an ENT and get specific imaging done to see if there is some obstruction or discoordination of swallowing that may be treatable. Speech language pathologists and ENT docs may use a technique called a cine-esophagram, which is a fluoroscopic movie of the swallowing mechanism and anatomy that can help to detect swallowing problems and how to treat them

You absolutely need to get this evaluated if it is causing her to decrease her intake in any way. Can start with your pediatrician, who likely will refer you to one of several specialists - possibly ENT, speech pathologist, swallow specialist. In meantime, note what foods are best and worst. For instance, can she tolerate liquids but not solids? Other way around? Does she also cough? ....

I agree, and a Pulmonary appointment is available on Healthtap to review your child's symptoms. A swallowing evaluation and chest x ray is recommended.