What was the last text Gabby sent her mom?

I’m a little confused about the timeline- was it actually Brian sending Gabby’s mom the texts about how Brian went to camp in the woods for the night, he said she could buy him out of the van, etc.? When I first watched I assumed it was actually Gabby, but just saw a post on here that it was Brian setting up an alibi to go with the $700 zelle (sick btw). Was it ever confirmed what her last real contact was?