A couple things...
PB had been in their lives for 18 months. May of 2009 is when she contacted DB/KB.
DB/KB had a presence on FB, because that is how PB found them.
Without being able to access the FB pictures in question, and without knowing what happened after DB/MJ got off the phone with each other, I have to draw from what JS said about her daughter. JS said that PB did NOT like conflict, was a peace maker, and did NOT like to get in the middle of things. PB did not want to confide in DB about being hit on and feeling uncomfortable because she did not want to cause friction between herself and DB/MJ, which made me think that the person who hit on her was in the apartment because he was connected to MJ somehow.
For these reasons, I find it difficult to imagine PB searching out this photo, and essentially instigating more conflict/stress in the household.
The revelation about the FB photo and MJ wanting to get back together is illuminating, but perhaps not for the reasons initially assumed by those who revealed the information....