Suzume knows how much baseball meant to Kenta and how much effort he poured into it. If someone you love is hurting you feel it too. Especially when she can't do anything for him at all.
Because while Momoko is supposed to be her "sister" Suu-chan never shows her real self to her or relied whole heartedly to her.
Suu-chan doesn't want to show her childish side and didn't order the cream soda. She hesitated to ask Momoko for help.
She wishes to be her sister but she'll never...