Yeah, I can see the logic behind Elf Onee chan's action, she's a notorious adventurer and the MC being in a party with her will be widely announced that if another adventurer mess with MC, her future husband, she's going after their head. And I'm glad the Elf won't be follow MC everywhere, she's will let him experience first and give some explanations or pointers later.
My only complaint is that maybe she should spend a few days tutoring him about swordsmanship because he's a fresh adventurer with no previous experience handling weapons.
Also no snuggling scene between those two, smh.