As MrTutle mentioned, she's the public moral committee who always scolded Nana for flirting with Ryuuji at school (but surprisingly was too innocent to understand what the two were actually doing.Who were you again?
Can't remember the bubble color either, but I do know this is the public moral committee (never remember her name though) so it has to be back in time; then the only person who has groped her has to be Nana.Took me a while to figure it out, public morals committee and the speech bubble is Nana's colour, hadn't seen her in so long I thought it was an aged up Mana chan but that wasn't the right name and Nokki didn't have a boyfriend so I didn't know who was talking (I will not remember speech bubble colours unless I'm binging chapters)
This is a flashback to the original characters, so it's high school.Aren't they in 1st grade?