Welcome Wojos,
Your wife has really been through the ringer. Sorry for her pain. I didn't see but, I am assuming she has had the cystoscopy done with a bright light and a thin snake like contraption? That is a normal test in looking into the bladder.
Sometimes a reason for bleeding is never found and there can be many causes. Also, a large amount of blood to us might be very little! As you said from infection to stones. My wife had an unexplained bleeding some 30 years ago and we never found a cause. She did have what is called a retropylogram. A test that reads up through the bladder into the kidneys and that almost sounds like your Feb 20 test. Hope you get some answers! Let us know what you find. We all learn from each other.