I am filing my tax this year and I am claiming my sister who came to the US on a student visa. She is currently going to school and she lives with me. My issue is that her entry Visa has expired but she has a valid I-20 /I-94. The tax people are saying that her visa is expired and she needs some sort of other identification. I keep on telling them they just need to attach a copy for her passport/i-20/I-94 to the W-7 .

It is clearly written on the instructions page 5 - line 6 c of the W-7-
She has not left the US since she came here . You have to leave the country to get a new entry visa- that's why they give you an I-20 to show that you are current student going to school and you are in the US legally.

They are asking me to provide 2 supporting document - I have her valid birth cirtificate , an expired passport and a valid I-20 and I-94 . I don't know what they want. What should I do?

I believe that I answered you on this in an email, but, to be safe, I will post it here as well:

What you should do is abandon the attempt to claim your sister as a dependent, as she is NOT eligible!

IRS guidance on this issue is clear: To be claimed as a dependent, the person being claimed MUST be a resident of the United States. The documents you cite (I-20 / I-94) clearly indicates that she is here on either a F-1 or J-1 visa.

That being the case, she is NOT a resident and thus CANNOT be claimed as a dependent.

Sorry!