I now detest when 2 characters meet and then we get the infodump they meet in their childhood and simply forgot each other, is a boring cliche and many times is forced, like it looks this time, made up just to make so that for MC she isn't a 1 month pal anymore.
And about her behaving differently afetr waking up, she didn't wake up, she just wasn't sleeping and heard everything MC and idol buddy said, possibly getting a bit annoyed at being nothing for MC.