Hi and Welcome to HealingWell, Leighanne!!
I'm sorry to hear about your daughter's heart health issues, it does sound pretty complicated and since none of us are Dr.'s here, we can only offer our opinions of things.
This must really be very stressful for you as well! I have 2 children myself with the youngest being a daughter of 17 - I can only imagine how hard this is on you.
I'm going to list a couple of links here that are extremely well known and reputable. Please check these out and see if any of this rings a bell or gives you a clue as to what might be happening with your daughter - have her read them as well.
You've gotten a lot of good advice above and I wholeheartedly agree that getting a second opinion, or 3rd as the case may be...could be extremely useful for your daughter.