I don't get what sheep means. Would someone tell me?

I'm assuming you mean the Christmas chapter, in which case;
Soushi said in a text that all men are wolves, implying that if she's not careful he'll pounce on her. Megumi then later said that she's a sheep, implying that she's ok with him pouncing on her, as wolves tend to eat sheep.
Hope this helps!

Now I get it. That makes sense. Thanks.