"Would a Liver Flush be dangerous for my mother who is 82? Her cholestrol is in the 300 or 400 range. "
No, but in her case, she should follow complete cleansing program: from parasites cleanse and Bowel Cleanse to liver flush.
"Another thought. Would lactose intolerance be related to liver/gallbladder problems, too?"
Intolerance to any kind of food is always related to liver and to gallbladder.
It is liver that gets all blood from the intestines (portal vein), and it is the liver that is suppose to process all foods that have been absorbed into blood stream.