Are the VA benefits taxable income ? If so are they more than $4,050 for 2016 ?
Your mother can be your dependent if she has less than $4000 of taxable income AND if you provide more than half her support.
Her support includes living expenses, medical care, entertainment, travel and so on. For living expenses, you take what would be the cost to rent a home like yours (not the mortgage payment) in your neighborhood and divide by the number of occupants. You can then add an equal share (sounds like 1/3) of the utilities, food, etc. Those are shared living expenses. Then add her personal expenses like medical care, travel, clothing, etc. That's her total living expenses. Then figure out if you provide more than half those expenses, either in money, or in kind (living in your home rent free).
There is a worksheet on page 16 here to help you figure it out https://www.irs.gov/pub/irs-pdf/p501.pdf
"She has in home caregiver which costs most the money she receives" That counts as her own support (not yours).
A person can be a Qualifying relative dependent, if he meets the 6 tests for claiming a dependent:
1. Closely Related OR live with you ALL year
2. His/her gross taxable income for the year must be less than $4,000 (2015)
3. You must have provided more than 1/2 his support
4. He must be a US citizen or resident of the US, Canada or Mexico
5. He must not file a joint return with his spouse or be claiming a dependent of his own
6. He must not be the qualifying child of another taxpayer
Social security and tax free VA benefits don't count as income, for the income test, but that money she spends on her self does count as support not provided by you, for the support test. Money she puts into savings & investment does not count as support she spent on herself. Note that a parent is closely related so there is no requirement that she live with you at any time, during the year. But if you provided a home it helps your support case, unless they own the home you live in. If no one person (or married couple) provides 50% of the support (for example your siblings are also sending support), then a "multiple support agreement” (IRS Form 2120) can be used, to allow you to claim the dependent.