What to do if my ex-spouse has full custody of my 15 year old daughter but she now wants to live with me?

Unless she is in danger, your daughter needs to return.  Most courts will not change custody this close to the end of the school year, so she needs to stick it out that far.  You should file to modify the existing order.  At age 15, she can tell the Court what she wants.  Failure to follow the order now, may jeapordize your ability to change custody later.  She needs to go back for now.  Call an attorney in your area for more detail.

If you and your ex-spouse agree to a change in your current custody/visitation schedule, you can file a joint complaint for modification in the probate and family court.  If you are not in agreement, you will need to meet the standard for a modification in order to have obtain physical custody or more parenting time.

Okay, I can understand how she may feel.  But if she does not go back to her Mother at least for the time being you would be inviolvation of the custody agreement and that could get you in to big trouble (unless of course it was for an emergency reason like abuse). Explain that to her.  She does not want to see you in jail.  Now, if she wants to live with you at this point you will need to file a petition to modify the custody agreement and to be the custodial parent.  Her testimony will be considered by a judge,  However, judges do not change agreement lightly and for frivilous reasons.  She can not say: becuase my mother is mean or she is too strict.  Courts can surely understand if she wants to foster her relationship with you.  They look to "the best interests of the child." Do not make up stories about her Mom.  It will only get you in to trouble.  Good luck.