Then she needs to amend and say NO to the custody question. She can either claim the child and ALL the benefits of remove the child totally, then you can claim on a mailed return.
If you both live with the child, you can agree who claims the child and all the benefits. The child can only be on one return and not on the other at all. The benefits cannot be split.
Per the IRS: in order for parents to split the benefits the parents must have lived apart at all times during the last 6 months of the year, whether or not they are or were married.
<a rel="nofollow" target="_blank" href="
https://www.irs.gov/publications/p501#en_US_2018_publink1000220904">https://www.irs.gov/publications...>
The dependent interview is confusing since it asks about custody without really explaining what that means. That can lead you to answer the questions in a manner that gives credits to both parents when they both live with the child which is not allowed. The child can only be on one parents tax return and not on the other at all.
*Only* divorced or separated parents that have lived apart for the last 6 months of the year can have a *custody* agreement. The parent that physically lived with the child is the custodial parent and the parent that did not live with the child the non-custodial parent. Under those circumstances the custodial parent can release the child's exempt to the non-custodial parent who did not live with the child with a 8332 form (which is a custody agreement).
When *both* parents live with the child, no such custody agreement can exist since both parents have equal custody and there is no non-custodial parent. The dependent and all the benefits can only be claimed by one parent.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**