Shade would never be able to say it without meaning it.
She is fine calling pokemon/ creatures cute but to say ‘I love you’ would be very difficult for Shade.
Her heart is incredibly complex with many secrets people have yet to know about Shade. Pretty much everyone has only seen one side of her and think she is a super cheerful and happy mega absol.
The fact of the matter is that she has many emotions in her and many concerns, worries and even fears or doubts.
For example, one secret nobody has ever found out, not even her own team. She constantly tries to lock it away in her mind as she struggles to find a mon she feels she can trust to tell it to. She did choose Ruin the zoroark in the end to pass her secret on to one day.
Put simply though, Shade struggles a lot with love and earning it with her can be very difficult. She might fall for someone herself but just to work up the courage to tell them will take a lot of time.