When they first went to Florida, they enrolled her in cyberschool and took her with them. But, they never had reliable wifi, so she failed school. So, 1. there is necesity.
But, personally, she had been coming over quite a few times a week for a couple years prior to the custody deal. Her parents initially wanted me to tutor her, so I did. But, she got excited about all my electronics. So, she'd get her lesson and could then try out some video games. This morphed into visits from the family, so the kid could just hang out. Then she started visiting on her own. Then she started staying for dinner.
Slowly, I started taking on care-taking roles. She had hand-me-down shoes that a teacher gave her. I took her out and got her new sneakers and just some junk clothing at Walmart.
I learned that she had missed out on quite a bit in life, so I started doing social stuff. She had been to the movies 3 times when I met her. So, I took her to see a couple movies. We went to the zoo. We went to a couple museums.
Then her parents asked if I could take her in. I set up a room for her, got the paperwork square with the school, and she was fine. She was in 8th grade then. So, she was a bit weirded out, but I made sure she could lock herself away in her room, gave her a phone so she could call her folks and all that.
Now she's nearly 17 and finishing up her Jr. year. She's fine with everything. Clearly, she's happier with her folks, but she has fun up here and is very comfortable. This winter we did a lot of art projects: crayon melting and a ton of sculpy clay stuff.
And now it's just normal. At first I didn't like having someone else's kid, especially middle school age, with me. It freaked me out, but I knew I was opening her up to things she had never seen and it was fun, too. Now that's older and I have years of documentation, I just have her tag along with me. If I'm going to Pittsburgh, I ask if she wants to come. If I'm going shopping, she usually tags along and I'll slip her a few bucks to get something she wants.
And the relationship is normal. When she was younger, you could see there was a little of that school-girl crush. Now she just treats me like a second father - and I even make those terrible dad jokes for her benefit. So, now that her folks are back, she lives with them, stops up 3 times a week to take showers for school and watch TV. And if something interesting is happenening on the weekend, I invite her, and she has about a 50% rate of tagging along for those things (I should add it's about 80% for shopping).