My ex husband had an ex girlfriend who did this. 6 months before we got together she said she was pregnant then 2 weeks later said j/k found the guy. Then 4/5 years later said hey she deserves to know her dad but only through social media so let me stalk you there. I told her that we will get dna through the court and if he is the dad then we will go for A psych evaluation of her and custody. She got scared and blocked us. That was 2011. In 2019 the “dad” who raised her got her a dna and said no more child support but I’ll hang out with you if you want. So she went looking for my ex. He was paying me child support to me so he told her to wait until 18 because of his job (he didn’t want to pay her support). Turns out she’s his! And I have guilt knowing that the mom abandoned her with the grandparents shortly after I spoke to the mom in 2011. Her life would have been better and she would have been raised with her half siblings. But the kids all love each other and enjoy hanging out and talking on the phone. I would threaten her with court ordered dna and do it and get her out of your life if she’s lying. If the kid is his get the kid in a custody agreement so she can’t play games!