Q. How do I go about making sure No one else claims her.
A. Basically, there is nothing you can do, other than asking her to file a Married Filing Jointly (MFJ) tax return.
If she does not agree, you must file as Married Filing Separately (MFS). You are not allowed to claim a spouse as a dependent. So, whether somebody else claims her doesn't affect your tax return.
If you file MFS, she must also file as MFS (if she has to file at all). Some coordination is needed between you. One thing: if you itemize deductions (instead of the standard deduction), she must also itemize, even if she actually has no deductions. If you live in a community property state, you must allocate your income.
