Here's what you need to do:
- Enter your child in the Personal Info section.
- When asked how many months he/she lives with you, DO NOT INDICATE THE WHOLE YEAR. Answer this question truthfully. It can be 2 months or 0 months- the child does not have to live with you for you to claim him/her as a dependent
- Continue and say "Yes", you have an agreement with the other parent
- Say "No", the child's other parent will not claim him/ her per our legal agreement.
Claiming the child as a dependent and living with the child are 2 separate and distinct tax benefits
As long as your ex didn't also claim the child as a dependent (which would have been her mistake), there is no conflict here.