I can't speak for momtective, but here is my take on this. No, this is not evidence that she knew before Dec. 23rd that EJ planned the SA trip. But it really has a "feel" (FWIW) that she knew all about it before hand. I just don't see how if Elizabeth lied to them on Dec. 18th and said she was taking Gabriel to see Logan, and then ends up in SA, that the Smith's would really be okay with that. And this message seems to portray that TPS had no problem with it and she even seems to be egging EJ on. The part about "we are going to be foster parents, his dad has decided to keep him" has always really bothered me too. I kind of take that as her saying that Logan has decided to keep Gabriel, and that is why they are going to become foster parents, and also why EJ took the trip. No, I don't think there is any evidence in this that could help in any court trial. BUT...to me, it speaks clearly that TPS was in no way upset about EJ's little trip. If I was set to adopt a child, had custody for 9 days, and the mother took off with him after lying to me about where she was taking him, I would be absolutely furious. TPS continued to stick up for EJ until it was clear that it was hurting her reputation and people were implicating her as an accomplice. THEN she changed her tune.
This is ALL just IMO, though.