My thoughts on this are so random that I can't keep them organized or articulate them correctly, but I try.
If I was to open my texting app, the default one, my texts would be in order. Whether sending or receiving. So, how far up in the texts to others would hs be that she would accidentally send it to him? I would guess nowhere near the top since she was with him last. ie... If I texted someone or many, say, Saturday til 1:30pm before I got picked up. And then theres an unknown amount of texts from others until 7pm Sunday, how far down should the person be in my texting app that I texted on Saturday.
I still can't see that hs was sent a text on accident. And I still can't see that she would send a random one to someone that just dropped her off. Unless she was checking in with hs, which I can't see either. So imo, hs created an alibi like a ws member mentioned or someone picked hs as to divert attention to him. Maybe a jealous boy.