Nitroglycerin Spray

My daughter (age 20) was recently prescribed nitroglycerin spray for chest pain. She is also an asthmatic. Salbutamol HFA, Oxeze, Advair and Singular are her asthma medications. She has no history of heart problems but does occasionally suffer from chest pain which they have not been able to identify the cause. She has been prescribed muscle relaxants and other medications in the past but none of these were helpful. The nitroglycerin medication is taken on a need basis only when she has pain and not prescribed to be taken on a daily basis. Are there any long and/or short term effects from using the spray? What happens when/if after using the medication for a few months she decides to stop? Thank you for taking the time to review my questions.