Any updates on your sister?
I would also not hesitate to request clarification on whether and how a passage could be created for the drainage of the menstrual flow, rather than going to hysterectomy. It would be a better option.
The uterus has life long functions; it isn't just for having babies. Its removal (hysterectomy) has some long-term and progressive problems including, but not limited to, displacement of the bladder and bowel which can cause life long issues with voiding including incontinence. And it has other anatomical functions. It also has hormonal functions in that its removal is associated with a fairly high risk of impaired ovarian function or complete ovarian failure which increases risk for a number of health problems such as heart disease, osteoporosis, hip fracture, Parkinsonism,dementia, impaired cognition and memory, mood disorders, eye problems, more severe hot flushes, sexual dysfunction. The younger a woman is when she has a hysterectomy and/or ovary(ies) removed the greater the problems tend to be over time. (The ovaries of a woman with all her parts produce hormones her whole life for good health.)
Hysterectomy is grossly overused in some countries.
From your explanation, it sounds like your sister's doctors have not done a very good job of explaining her condition nor the short and long-term risks of her treatment options. Have they used a diagram of the female anatomy to explain what is missing? For example, does she not have a vaginal canal or does she have one but it is blocked / closed off?
It would be a good idea to get some clarification and then do your own research into treatment options and their risks and benefits. Best of luck to you and your sister!