Well it seems to be that her dad explains that while the other 4 girls were accused of staying overnight at fans place, Uitan did not. Nor did she have any "secret contact" with some fans.
Here's a scan of the newsarticle:
In upper right corner, is the two mails she received on August 16th, from a fan, that her dad is showing. The sender is unknown, and she thought it was someone from HKT48, and thus answered. But after two-three exchanges and noticing that it's not an HKT48 member, she decided to ignore it.
But somehow staff knew, and Uitan got booted as well, and her cell phone was taken after the performance, by staff.
Uitan was calling her parents that evening, crying, telling them she wasn't continuing in HKT48.
The day after, HKT48 staff gave a cancellation form to sign for her parents, without explaining much at all.
He says staff seemed eager to cancel the contracts as soon as possible before Tokyo Dome concert. Father says after the conversation he had with his daughter, he wasn't convinced of the story and the cancellation form, so declined.
Then later an AKB manager had an interview with his wife and daughter, and his wife signed the cancellation note, also under his name, while on phone. After this there were no contact with staff.
Father says there was no contact with this fan who had acquired her phone's email address, aside from the few replies she sent.
He is angry that the official announcement was that Uitan herself had chosen to leave, which was absolutely not the case at all.
Magazine has asked staff, which denies everything.
Uitan herself will be focusing on school work now.
So in short it seems that while there was a reason to fire the other 4 girls, if we go by what has been stated before, there was no real reason to fire Uitan, but apparently she had to go as well.
Here's short tweet translations of the above, from AKBWrapup:
Shunkan Bunshun report: father of former member of HKT, Komori Yui, accuses of AKB management, claiming it's unfair treatment.
Summary: In simple words, most of HKT members were chatting with fans through messenger function on google plus.
Those members got yellow cards from management. In the middle of Aug, the 4 members stayed at fans room, gave Komori's mail address to fans.
HKT's manager saw messages from fans on Komori's phone, and recommended her to leave the group.
Then Togasaki came to her parents, asking them to sign a document of consent to fire her.
Her father refused to sign but her mom signed it on his behalf. She's left the group last month, and now her dad accuses of AKB.