kid's 2nd 485

My daughter already filed her 485 together with me last year(EB2). My exhusband is going to come to the USA soon. He wants to include my daughter as his 485 derivative so that my daughter can get her green card much quicker for her college application(My exhusband got his EB1a approved). I have some questions:

1. I am the sole legal and physical custody of my kid when divorced. Should we change to joint custoty so that my daughter can be my exhusband\'s 485 derivative? or Can I just give a written permissioin to permit my exhus to include my kid as his 485 derivative?

2. If my daughter is going to be my exhus\' 485 derivative, which one is better, file a complete sepreate 485 for my kid or relink to her already filed 485?

Thanks