To clear things out, she didn't "run into" her. The staff for メダマ!? invited Reina as a surprise, after Saito had declared her love for her. At the show before Reina's surprise, Saito had also described her ideal clothes and accessories for Reina to wear. So, naturally they also prepared the mentioned garments.
Saito did not have her own copy of Re:, she got it from Reina at the radio show. As a second surprise Reina agreed to dress up according to Saito's request, but to further make Saito a bit more pumped up, she had to do a Hello! Project quiz in order to show off her love and see Reina again. She barely finished it thanks to her nice partner, but still. At the end Saito also got to fulfill one of her cosplay dreams.
「舞子お姉ちゃん、こんなれいなでも大丈夫?」
After the show Saito got tickets to a MoMusu concert from the company and attended the 5/17 one. A month later and she makes it public on アナ☆ログ.
Notes: She's not really as hardcore as one might think.
* She called Sayumi "Sayuri".
* In confusion she insisted on Rika/Yossie being in Love Machine
* 6th gen joined in 2003, but she said 2002. And the -kkies suffix appeared before 6th gen joined.
* She totally failed singing the first part of Romantic Ukare ModeIn other words, her eyes are all on Reina only.

She's still an awesome announcer, though.