My 15 yr. old has nasal polyps, frequent nausea, high blood pressure, acid reflux, chronic sinusitis, she's short for her age, had sinus surgery, a REALLY hard time breathing 24/7, a cough that gets worse after eating, etc. The ENT clinic said she had asthma but she has never had an attack. I've heard that when a child/teen gets nasal polyps it is almost always associated with cystic fibrosis. Could she have this? What are the chances?

Not 'almost always' but possibly around 2/3, depending on the research you read.
She can be tested by something called a sweat test. You can try to get medical history from all relatives on both sides.