Hi Daisy! I moved your thread here because we have a whole subforum to deal with what happens to our bodies and heads after weight loss.
Take a look at this sticky:
Weight Loss And Skin FAQs and maybe it will answer some of your questions.
My suggestion for your sister is to make an appointment with a plastic surgeon for a consultation to get some answers to her questions. Her weight loss is just amazing and I suspect that only someone who's skilled in dealing with such large weight losses is going to be able to give her the information that she needs.
Congratulations to your sister and

to you for being such a good sister!