I am going through something similar and can relate. In ways of support, depending on what type of person your SIL is she may need help navigating assistive technology, medical appointments, state services, and career planning, among others. In addition, she will need emotional support most of all. Understand this is a mental journey more than anything else. Make sure you are the one offering support and taking initiative rather than waiting for her to ask. If it looks like she's having trouble doing a task due to vision, ask her if you can help. Vision loss is a broad term, and different diseases cause vision loss to develop differently. She may become light sensitive, have reduced vision in her periphery, reduced acuity, or a combination of these symptoms. This is a big deal for her and it is sometimes easy to ignore or trivialize the problem since it is not easily visible to others. Do your research on what is causing her vision loss, and, if the cause is believed to be genetic, get genetic testing done at her earliest convenience (since testing will strengthen the diagnosis, can take a few months to complete, and is required for any sort of gene therapy clinical trials).

You all have a long road ahead of you. Take it one step at a time, and pm if I can help provide additional direction.

Edit: also know that by posting and taking steps to help her you have already done more than most others would

What is the eye condition she has? When i was 21 I was diagnosed with Retinitis Pigmentosa and told "YOU WILL BE BLIND BY 30" I am now 42 with pretty good central vision in my right eye and about 6 dagreesa of peripheral vision.

I recommend contacting a local organization for oriantation and mobility and getting a white cane to beat of all the haters...

>Does anyone else

Probably