Since your situation doesn't involve a prior court-issued custody order, it seems that you will either need to work it out with the father, or (you or he could) take the issue before a court of law. Courts will often listen to your daughter's preferences, and will make a decision based on the best interests of the child. Talk with your daughter and listen to her reasons for wanting to go, and let her hear yours. Talk with her father, and figure out what to do that would be in the best interests of your daughter. Things like how you and she would maintain your relationship and how things might change due to distance, how much time dad can spend with her, schooling, supervision (homework, etc.) and other issues come to mind.
The above is not intended to be legal advice, but may be used for general information. Please contact an attorney for specific help tailored to your needs. www.figgardenlaw.com
Children do not make decisions regarding where they live and how they are raised. Parents have a responsibility to make those decisions for them. If a custody case were filed, the Court would consider the 15 year old's wishes as ONE of the factors to consider in determining what sort of custody arrangement is in her best interests. However, until she is 18 she does not have the final say.
What you need to do is to talk to her father and determine, hopefully together, what is in the child's best interests. That is your responsibility as a parent.
You can reach Harkess & Salter LLC at (303) 531-5380 or info@Harkess-Salter.com. Stephen Harkess is an attorney licensed in the state and federal courts of Colorado. This answer is for general information only and does not create an attorney client relationship between Stephen Harkess or Harkess & Salter LLC and any person. You should schedule a consultation with an attorney to discuss the specifics of your legal issues.
You have done a great job for the past 15 years and now she wants to get to know the other parent. This is pretty normal developmentally for 15 year olds. It would be best to work out an arrangement with her father, keep this peaceful and support her, if her father is able to provide a safe, supportive and loving environment. Make sure that you get an agreement in writing and file it with the court. You also should know that once she has lived out of state for 6 months, her new state will have jurisdiction and Colorado will not be the place where you go to court, unless you file now while she is still living here or within six months of when she leaves.