Hi Jayada123123, I'm so sorry to hear you are going through such a difficult time. I do hope things improve for you soon. I just wanted to add a couple more pieces of information.
Unfortunately, the IRS is a bit backlogged at the moment, so things are taking quite a bit longer than they may have in the past. When the IRS does process the return you mailed, which could take quite some time, they will likely mail a letter to the mother, asking if she would like to amend her return, or file additional information as you did. If the return is not amended within a certain time frame, they will begin an investigation, or audit, to determine who is in the right. It may take a couple of months from that point before you hear from them about the audit, and it may take considerable time to be resolved. Its important to keep in mind that the IRS considers a child to live with you/qualify as a dependent if they were kidnapped by a non-family member. (Or at least the authorities believe that to be the case. ) So its possible the IRS may rule that the mother is not allowed to claim her as a dependent, but may also not allow you to do so either. Its in their hands now. I agree with SoCalGal22's advise to get a tax lawyer involved. Best wishes for a speedy outcome for you.
As far as preventing this from happening again, there is little that can be done, either by you or the IRS, to stop someone from filing a tax return for any given social security number. If it turns out the mother filed fraudulently, there would likely be a penalty to her, which may be an incentive not to do this again.
Are you certain it was the mother who filed the return? I know the IRS does not give out that information. It may be worth considering if it could have been a case of identity theft. If it was an identity thief who filed for your daughter's social security number, you could report that to the IRS on a form 14039. In that case, you might be able to get them to issue an Identity Protection Pin Number for your daughter. These are renewed annually. You would have to wait until you received it in the mail each year to file your taxes, but nobody else would be able to file for her.
