Greetings, and thanks for the question. I'm sorry to hear about your horse,s condition. What she is experiencing is commonly known as "choke". This is not an uncommon condition, and is not normally life-threatening. Firstly, I recommend to NOT try flushing it out with a garden hose. This could accidentally lead to inhalation of the water into her lungs, and create a condition known as "aspiration pneumonia". In order to fully answer your question, I need a bit more information from you, please.
1): How long has this condition been present?
2): How old is your mare?
3): Do you know what is lodged in her throat (excess grain, apple treats, etc.?
4): Is there any type of discharge coming out of her nose?
5): If you feel along the left side of her neck (where the esophagus is), can you feel an abnormal bulge where the feed/object is lodged? One of the more common areas is closer toward the chest, at the base of the neck.
Thanks, ***** *****'m looking forward to hearing from you.
-Dan C., DVM