Sora didn't really have time to get a first impression of Miyako when they first met. With all that was going on, Sora's mind had zeroed in on the prospect of meeting Piyomon again and Daisuke, Miyako, and Iori may as well have been one person at the time for all the attention she spared on them initially.
Hearing Mimi's words come out of the younger girls mouth on the other hand brought Sora's attention straight to the girl in front of her. Although first impression wise Sora couldn't really say, Miyako was the first of the new Chosen Children to make an impression on her.
The more Sora got to know Miyako the more she found herself amused by the girls antics. Miyako was emotional and active in an entirely different way from Mimi. Mimi was active when necessary, Miyako was active all the time. The girl only seemed to slow down when she was depressed. (something Sora doesn't specifically like letting her be)
Sora really wants to be a good senpai for Miyako, being one of the most emotionally mature of the initial seven Chosen Children, Sora remembers intimately the fear that there was no one bigger or stronger to help. That they were alone and worst of all, it was her responsibility to make sure everyone was safe.
If someone was injured, she'd often blame herself for not being capable enough to take care of them.
She was bigger and stronger now and she wouldn't let any of her kouhai's experience that fear if she could help it.
All the same Miyako has one of those fun personalities that drag you in and keep you, making it incredibly difficult for Sora to stay totally mature in the younger girls presence.
Altogether she's really happy she was able to befriend the girl and wants to help her no matter what.