welcome to beyond blue.
I want to thank you for the wanting to the help your sister - not everyone of like that. I think the best place to start would be here...
there is also a K10 test on the beyond blue web site as well to look at. Perhaps the one thing that helps is listening, and I am sure from your post you would be doing that. There are probably lots of tips that could be given, but I would probably give you information overload.
If you have any questions, just reply and I will get back to you when I can.
It is wonderful you are wanting to help your sister. I'd like to just suggest one thing, it may be that your sister is not really sure what is actually causing her anxiety, just that she experiences it.
It may take a professional to help her to recognise and understand what issues may be causing her reactions to turn into anxiety.
From what I have read, there are different types of anxiety as well. The more you read, the more you will understand and be able to assist her. You may like to look at beyondblue.org.au/types-of-anxiety.
Wishing you both all the best, from Dools