Ok so I’m supposing that the mother is a “reverse-love” kind of character as in she already knows and has scouted out the girls. She is just playing “innocent/cute” but then will come in with “DON’T TRY TO SEDUCE MY CUTE SON WITH SUCH WEAK TACTICS” or something like that.
We've already seen that she wants him together with one of the girls (doesn't care which one) to the point where she's willing to spill on his (supposed) masochist tendencies if it gives one an in.