Losing Weight Too Fast?

I recently taught a friend about proper nutrition and exercise. She’s doing great, but we’re both concerned that she’s doing too well, because she’s losing 6-8 lbs a week, rather than the recommended 2 lbs per week.

Here are some important considerations:
Starting stats: 5′4"/235lbs
Age: 26
Had her gallbladder removed in January.

She’s not on a crash diet or anything: we actually planned for her to lose at a rate of 1-2lbs per week, but her body just seems to want to dump more. She’s getting good quality calories, and moderate exercise.

Is this healthy? I’ve heard something about pancreatic problems arising from this, as well as bone density issues. Can anyone give me advice on this, or point me in the right direction? This is all I’ve found on the issue: How To Lose Weight Fast and Safely – Exercise, Counting Calories, and More