She can choose implants. Saline is an option along with silicone. She can also choose to use inserts or prosthetics.
I had my double mastectomy last month, and right now I’m seriously regretting reconstruction. I don’t know, but I was so confident going into the surgery, but I waffled everyday about the reconstruction.
I had expanders placed during the surgery, and they’re supposed to start filling them next week. These past couple weeks, I’ve had two major meltdowns about the reconstruction process. I wish I would have waited and given myself more time to process and choose. They saved my nipples, but even that healing process was awful, at least for me. I had to use nitro paste for about 5 weeks, and it gave me terrible migraines on top of the normal post-op pain, muscle spasms, and nerve pain. It worked, but I would have done without that if I knew how bad it would make me feel.
This is my story, but I share it as my story only. The best thing you can do for your sister is to empower her by being by her side, being a second set of ears, and allowing her space to think, decide, research, and ask questions.
Many women feel more empowered and comfortable with themselves after reconstruction, and I have nothing but love and respect for those women. If she does choose implants, she will have surgical drains at some point. Those can take 4 weeks to come out. If she goes flat, nipples or no nipples, she won’t have drains. She’ll have a shorter recovery, and she can use prosthetics or inserts. Or she can rock the flat look.
Whatever her choice, she will need a lot of support.
Sending hugs.

Wow. Good luck. Such difficult ideas to decide on. I had DIEP. But if anything, I'm underweight. So glad that I did something. My primitive brain has decided that I'm female again.