The ultimate decision is up to your sister as to will she ride again or not. It is your job, along with husband to support her in whatever route she goes.
I was hit in the mid 90's (Driver ran red light, no insurance) which resulted in multiple operations and 13 months of recovery, and medical bills that put me in great debt for over 10 years. But for me never once did I want to stop the sport I've grown to love, and was back on the bike a year and a half after the accident. It did end me racing competitively, and I do live with daily back pain but I Love the freedom my bike gives me to much to stop.