Without knowing the specifics of your case, I will say that generally one can file a motion with the court to modify an existing custody order. The court will make its decision primarily based on the best interest of the child, so you'll want to focus on that in your motion. List all the reasons that it's in the girl's best interest to live with you and her father, not her mother.
A few things you should know. There are two standards that the Court looks at when it comes to child custody orders. The first is the best interests of the child standard. That standard is primarily at play when it comes to temporary orders (aka pendente lite orders). The burden of proof is not that high. The Court makes its orders regarding modification of custody on the basis of what is in the best interests of the child (there are multiple factors that go into the best interests of the child analysis).
However, if it was a permanent custody order pursuant to Montenegro vs. Diaz, then you would have to show a substantial change of circumstances to modify custody. Now, to modify visitations, whether a permanent order or otherwise, you may not have to show a substantial change of circumstances, but for custody, you would have to do so, otherwise the Court will likely deny the request. To make a showing of a substantial change of circumstance to justify the modification of custody, the burden of proof is much higher than the best interests of the child standard.
The above materials do not constitute legal advice or opinions and should not be relied up on as such. Transmission of the information is not intended to create, and receipt does not constitute, an attorney-client relationship. Please seek professional counsel as nothing contained herein is intended to be a substitute for legal counsel.
ON THESE FACTS, A RELATIVELY SIMPLE MODIFICATION REQUEST CAN BE MADE. HOWEVER, THE TOUCHY PART IS WHEN THE MATTER IS HEARD. YOU ARE SUBSTANTIALLY CHANGING THE CURRENT ORDER, BUT WITH APPARENT GOOD REASON. DEPENDING UPON THE CHILD'S AGE, THE COURT MAY MAKE SOME INQUIRIES OF HER AS WELL. IT APPEARS THAT YOU HAVE A GOOD CHANCE OF SUCCESS.