Thanks for your kind words!
I was formally diagnosed as hypothyroid in 1995, long before I lost the weight. I've taken synthetic thyroid hormone -- either Synthroid or Levoxyl -- since then so I was on it when I lost the weight in 2001 - 2002. Sadly, I've never had unexplained weight loss, like your friend! It can take six months to tweak a dose of Synthroid to find the correct dose, but once it's found, your friend should feel a lot better.
About metabolism ... cardio can boost metabolism temporarily (for a few hours after exercising) but our metabolisms can be permanently
boosted from building muscle through weight training. Muscles are the calorie burning furnaces in our bodies and burn calories 24/7/365, so the more muscle we have, the higher our metabolisms are. That's why it's crucial to weight train during weight loss in order to prevent the loss of our precious muscle mass.
Best of luck to your friend!