Tax question. My ex wife moved out. We are not legally separated. She filed both of our taxes. When filing she filed me as "single."?

I do not know what she filed herself as but she did claim our daughter. Question 1: Can I file an amended tax return? Question 2: If she received a refund and since we are still married will that refund be split? I am currently paying in 4k to the IRS. Any information would be appreciates.