I don't really get this scene, I was hoping the LN would give more context but my read so far it seems as though the manga adapts the LN 1:1. Renako suggests them being Rena friends, then asks "what do you think?", Mai says that it is unreasonable, then Renako has some internal monologuing, and then asks Mai again "What do you think?" and suddenly Mai is more open to the idea.