Responses
The pink diamond reminds me of
https://www.mangago.me/read-manga/isn_t_being_a_wicked_woman_much_better/
Yes this is it! Thank you! (≧∀≦)
It's a webtoon adapted from a novel. FL got transmigrated where she is a noble. I remember that she has 3 brothers. 2 older then 1 younger. She opens a cafe and had her 2nd brother make all the equipments like a blender. ML is very pretty, leader of a student council (?), and has strong powers. I also remember something about a pink diamond arc thingy.