There was a theory knocking around that she's Carla's mom aged 20 years and that she and Miranda had matching necklaces (perhaps Lynette did too and it could be among the clothes that was part of MC's inheritance) but if Miranda has died like Lynette she could've left Bianca the necklace, that could also be the route for MC to discover more about that side of the family if he finds Lynette's necklace then sees Bianca (or even this teacher) wearing the same necklace.
Then again MC doesn't realise a house that he had a memorable picnic in sight of, that he has a picture of Jill in front of and (presumably, because we don't actually see the house in the scene iirc) had dinner at is the same house as is in Lynette's photo so the chances of him recognising necklaces as being the same is quite unlikely.