I think that the sister can use a good headbutt. "I decided to interfere." Cracks knuckles, interfere this! BONK ...
Honestly, I don't think Sara can offer anything to Mei other than infatuation. That's. About. It. She obviously knows next to nothing about Mei and when faced with her personality, past, and all that mumbo jumbo, what she offer her? It was preetty clear that Sara no good with Mei asking if she is needed, not the other way around. To top it off, the sister clearly missed the mark when she overheard Yuzu and Mei's conversation in the litter park area but not understanding the undertones that there is a pretty clear history between the two. In the end, she just set up her sister to be used and possibly heartbroken.