I don't know about that... That would make sense if she'd otherwise distanced herself from Ron and his family but she didn't, she made plenty of statements about how the kids were so well cared for by Ron and Misty, and implied that she had been a close observer of Ron's family life to know that. Supposing Ron and Misty didn't get all those pictures on Monday 9th of February she would have known that they were there from her previous visits even if she'd been elsewhere on that day.
If it was an alibi it might have been meant to convey, "Look, I brought this picture with me, so it means that I must have been at home when Ron called, doesn't it?" If in fact she was somewhere else than her house. The reasoning being that she would likely keep an 8x10 photograph on the wall in her home and not with her at other times. But that would require forethought and planning (to have the picture ready in her car) and wouldn't apply to an improvised coverup, except maybe if TN came from Annette's at Welaka and actually grabbed one of Annette's pictures of Haleigh.
I don't know. IMO the photograph might be just a part of the "concerned grandmother who has LE ties" decor.
And also, if she knew that Ron and/or Misty hurt Haleigh, bringing the photograph would be a way to try to influence LE into the stranger abduction frame of mind. You only need a photograph to find a child who was abducted and is still alive and moving about with strangers. Whereas if your relatives have chucked her lifeless body in a dumpster, a photograph is probably useless by the time she is found, and LE tends to pick up any bodies they find at landfills anyway, regardless of whether they maybe used to look like someone they're searching for, before decomposing. (Sorry for being so graphic. )