Because although Greta had heard from the women inside that Orion wasn't easily swayed by physical beauty, her own observations and confirmation were an entirely different matter. She had known Orion for a long time, but seeing it with her own eyes was surprising.
Also, as one of the few people aware of Orion's memory loss, she couldn't help but wonder if those women were taking advantage of his vulnerability.
In particular, she found Celeste's behaviour concerning, as she doubted any young man or adult would choose to engage in such a childish act as having kushi with their mother.
