Pacchi's case

I'd really liked this episode. It was mostly about the bond between Posuto and Pacchi, which was really sweet and I somehow envied them their bond.
But I don't really understand Donki and her 'happiness is painful'. Okay she loves to be with her friends, but she had a chance to get real family and she turned them down. It is somehow not real for me. I can understand that she misses her true mom but she already should think about her future.