you know, i think the simplest answer is the most likely, that she sent the text.
He just isn't that smart imo. and there isn't any reason to send a text at 2 while having "seen" her at 3 or 3.15. It doesn't give him a better alibi or lengthen the time frame and i don't care how many true crimes he has read about, sending a text an hour and a half before you last saw her doesn't help
If he is involved it could be more like between 3 and 4 when DD saw him, maybe he stashed her in the shed and then cleaned up.