THEN, from about 2006, my ankle started to get very painful & was diagnosed with arthritis by an orthopaedic surgeon who suggested an ankle replacement. I had the surgery in May 2007 & was in a 1/2 cast again for 2 weeks with leg elevated. Then I was put in a "moon boot" but still not able or allowed to walk on my ankle. The moon boot is able to be taken off at any time so showering, etc is easier. Then the moon boot came off after 8 weeks, some physio was had & it's great now.
I forgot to say how long I was in casts & not able to walk during the first break in '94. It was 8 weeks.
The ankle replacement was 10 weeks.
I had no problems at all with DVT in keeping my leg elevated & sitting still most of the time. I did though, wiggle my toes a lot to just sort of keep something moving. It hurt a bit for a start but it got easier.
Waiting for a broken bone, (especially a leg or ankle bone), to heal is a waiting game. You can't hurry it. At the beginning, it hurts so you're quite happy to sit & not move. Then you don't want to sabotage the healing by walking on it too soon, etc.
DVT is very, very rare in a person sitting with a leg elevated in a cast my surgeon said. So you need not worry. Under no circumstances should your friend walk on her leg until the doctor says she can. This can be up to 8 weeks. Look upon it as a nice, relaxing holiday where she can catch up on reading & day dreaming & resting. Remember, her body has had a huge shock in having the bones broken, then having surgery & a pin inserted. The weeks are for her body to heal & regenerate, she needs all the rest she can in the first few weeks.
Unfortunately, the last couple of weeks can be a bit frustrating as you feel better & stronger & you want the cast, or whatever, off NOW & be able to walk normally again. Rather like an overdue baby, you want it out now! LOL.