Can I claim my sister as a dependent if I am paying for her college tuition? She is 25 and not being claimed by my parents

[jievin]

I have a green card but she doesn't

[LinaJ2018]

First of all, your sister has to be a resident for tax purposes ( although she doesnt have a greencard, if she stayed in US for at least 183 days during 2015, she is considered as a resident by meeting the Substantial Presence Test  )

Next, for her age, there are four tests must be met for her to be your qualifying relative for dependency

1. Not a qualifying child test,

2. Member of household or relationship test,

3. Gross income test, and

4. Support test-SupportWorksheet 

If she met all four tests, you can claim her. 

[said-el-nahas]

In general yes. Her legal situation does come into play unfortunately. Please see here how the IRS defines a qualifying relative.

Qualifying Relative

Many people provide support to their aging parents. But just because you mail your 78-year-old mother a check every once in a while doesn’t mean you can claim her as a dependent. Here is a checklist for determining whether your mom (or other relative) qualifies.

• Do they live with you? Your relative must live at your residence all year or be on the list of “relatives who do not live with you” in Publication 501. About 30 types of relatives are on this list.
• Do they make less than $4,000? Your relative cannot have a gross income of more than $4,000 and be claimed by you as a dependent. 
• Do you financially support them? You must provide more than half of your relative’s total support each year.
• Are you the only person claiming them? This means you can’t claim the same person twice, once as a qualifying relative and again as a qualifying child. It also means you can’t claim a relative—say a cousin—if someone else, such as his parents, also claim him.