BAnanas, you and I could be speaking of the same family. My son's ex has admitted to me she deliberately got pregnant with my GD to keep my son. She was 19 he 21. He did everything he could, struggled to get a mortgage and bought a nice house, was a great hands-on Dad, but she left him two years later for her ex boyfriend, who she went on to have another child with and since has married. My son was devastated.
She has behaved very immaturely over lots of issues. She doesn't seem to realise that she has no respect from my GD who prefers to be with my son though he is the disciplinarian, he spends as much quality time with her as he can, when work allows, so they do fun, age appropriate, things together. Whilst her mother wants to be her 'friend', letting her stay up late, watch inappropriate TV films etc and buys her (in my opinion) grown up technology to win her over.