Let's consider the actual rules. They are in publication 501.
https://www.irs.gov/pub/irs-pdf/p501.pdf
There are two types of dependent, qualifying child and qualifying relative. Qualifying child will allow the person claiming the child to get up to $2000 in child tax credit, but that requires income earned from working. A qualifying relative gives a $500 tax credit. Your mother (the child's grandmother) can only claim the child as a dependent if all of the following conditions are true.
| To claim as Qualifying child |
To claim as Qualifying relative |
| The child must live in the same home as the grandmother for more than half the nights of the year. |
The child and grandmother do not have to live together. |
| The child didn't provide more than half their own support (such as, from working). |
The grandmother must pay more than half the child's total financial support, and the child's taxable income must be less than $4700. |
| If the child lives with the grandmother and one or both parents in the same home, the grandmother can only claim the child if the grandmother's income is higher than either parent. |
The grandmother can't claim the child if any other taxpayer (usually a parent) can claim the child ahead of them. |
| If the child lives with the grandmother and one or both parents in the same home, the grandmother can only claim the child if neither parent is a taxpayer. A taxpayer is someone whose taxable income is more than $13,850, or their income is less but they file a return to claim any other credit or benefit. |
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Your mother might be allowed to claim the child as a qualifying relative dependent ($500) but only if she provides more than half the child's total financial support (the support provided by the grandmother must be more than the total of all other support, including SSDI or SSI in the child's name, money that you pay to support the child from your SSDI, other government and charitable assistance, and child support from the other parent.)
Your mother probably is not allowed to claim the child as a qualifying child dependent unless you all share the same home. If you do share the same home, and you are not a "taxpayer" (because your taxable income is so low that you don't file) then it could be perfectly legal for your mother to claim the child.
There is no way for you to know what is happening with her tax return, taxpayer privacy laws prevent it.
There is not much point in filing a fraud complaint, especially since (if fraud did occur) you agreed to it. If you don't have more than $13,850 of taxable income, or at least some income from working, you did not lose anything by not claiming the child yourself. In the future, the best way to prevent someone else from claiming your child as a dependent improperly is to file a tax return and claim the child yourself.
If the IRS has delayed paying her refund, it might be due to the dependent issue, or something completely separate. It would be best to let the IRS and your mother work it out without your help or interference.
