It sounds like you and your daughter did not live with your mother-in-law. If that is the case, and your daughter lived with you, then you can file an amendment to claim your daughter.
https://ttlc.intuit.com/replies/5187060
Consequences: The IRS will contact the mother-in-law at some point to let her know someone else claimed your daughter and that they may need to review and correct their return.
Instructions for amending your return are shown below for you. Also, this return must be amended, completed on 2014 software or IRS forms. An amended return must be mailed so include the original W2 copy, a copy of the social security card of the child and birth certificate as well as any records for that time showing you both had the same address. This could be legal, medical, school, childcare, dental or other records showing the address for both of you at that time.
You may want to amend your state return as well. Check your state information for whether it would be helpful for you.
https://ttlc.intuit.com/replies/3288565
