Hello lisaloves: I see this is your first post here on PC. So... welcome to Psych Central. Since you're here for your sister, the Partners of People & Caregivers forum may be of interest to you. Here's a link:

https://psychcentralforums.com/partn...ivers-support/

The depression forum may also be of interest:

https://psychcentralforums.com/depression/

By SAD I presume you're referring to seasonal affective disorder. So here are links to 6 articles, from Psych Central's archives, on the subject along with links to 4 articles on how to help someone who has depression:

Seasonal Affective Disorder

Self-Help Strategies for Seasonal Affective Disorder

Are You SAD This Winter? Coping with Seasonal Affective Disorder

https://psychcentral.com/lib/3-perva...tive-disorder/

https://psychcentral.com/lib/10-thin...tive-disorder/

https://psychcentral.com/blog/6-kind...al-depression/

https://psychcentral.com/blog/6-thin...hos-depressed/

https://psychcentral.com/blog/tips-f...dium=popular17

https://psychcentral.com/blog/3-ways...th-depression/

https://psychcentral.com/blog/9-ways...th-depression/

I hope you find PC to be of benefit.