received a notice CP87A from the IRS. They say my child cannot file a return if I claim her on my return and want her to amend her return. She checked the "someone can claim you as a dependant box. she made less than 2000 dollars.

Thank you but I just talked to the IRS and both forms are correct, no one else is claiming her, yet they state that she cannot claim file the return if I claim her.

Again ... if she filed as a dependent and you correctly claimed her then you will do NOTHING.  It is possible that you BOTH filed correctly  and ... there was another  person that claimed the child ... probably by mistake  or someone did it on purpose ( hello ID fraud).  SO if you are correct then you will do nothing at this time. 

From the link I gave you :

What you need to do

• Compare the social security numbers from your notice with the social security card for each dependent or qualifying child you listed on your tax return.
• Review the rules for claiming each dependent or qualifying child. After reviewing the rules:
  • If you find you’re entitled to claim the dependent, you don’t need to write or send anything to us.
  • If you find you listed someone who doesn't qualify as your dependent or qualifying child, you must correct your return by filing a Form 1040X, Amended U.S. Individual Income Tax Return. The instructions for this form will guide you through the steps to correct your return. Mail your amended return to the IRS service center shown in the instructions.

If it was not the child claiming herself then it was SOMEONE ELSE ... most likely someone you both know HOWEVER it could have been a complete stranger ...

If your Social Security number is compromised and you know or suspect you are a victim of tax-related identity theft, take these additional steps:

• Respond immediately to any IRS notice; call the number provided.
• Complete IRS Form 14039, Identity Theft Affidavit. Then print and mail or fax according to the instructions. 
• Continue to pay your taxes and file your tax return, even if you must do so by paper.

Additional Resources

The IRS has a host of useful information and resources on tax-related identity theft:

• A special section at IRS.gov dedicated to identity theft issues, including YouTube videos, tips for taxpayers, and an assistance guide.
• For victims, the information includes how to contact the IRS Identity Protection Specialized Unit. For other taxpayers, there are tips on how taxpayers can protect themselves against identity theft.
• Taxpayers who may be at risk for identity theft (for example, your wallet, purse, or computer was recently stolen) should visit the IRS identity protection page.
• If you receive a suspicious email that appears to be from either the IRS or an organization closely linked to the IRS (such as EFTPS), visit the Report Phishing page at IRS.gov.
• Click here for general information on how to report tax-related fraud to the IRS.
• To prevent tax-related identity theft, see Protect Yourself from Identity Theft.

These sites can help you understand identity theft and how to protect yourself:

• FTC Identity Theft Resource Center (www.ftc.gov/idtheft)
• Identity Theft Resource Center (idtheftcenter.org) 
• OnGuardOnLine.gov