We don't know. The facts, and I linked to the public record court documents in the last thread for anyone to read, are that: CT was taken away from DNV at birth due to marijuana in her system. C was returned to DNV at one month. In 3/2015, TT filed a petition for custody against DNV accusing her of being an unfit mother and a drug user, attaching pictures that he alleged show DNV doing drugs and drinking with C around. The judge set a hearing and neither party showed up so the petition was dismissed. The parties may have set a voluntary custody arrangement at that point, or CPS/the guardian ad litem/etc may have filed a sealed case and there are sealed proceedings we don't know about.
I focused on this because the question of custody has never been answered and the evidence shows it was not solely DNV's choice. There was a very aggressive petition accusing her of illegal drug use filed publicly.
@ChiCubs2016 suggested, and I think she's right, that since DNV/TT were on and off again, they may have broke up causing this aggressive petition and then gotten back together causing neither party to show up at the hearing.