Hello and Welcome to Justanswer, My name is Steve and I am here to try and assist your with your question
I do not believe it is the trans.
If it was it would restart no problem and you would not have had to have it towed.
There is another concern I have seen many times after raining.
The computer that controls the engine will fill up with water and cause this concern.
What you need to tell your mechanic to do is to remove the computer that controls the engine and trans and tip it side ways and see if water comes out of it. Or take it apart and see if there is evidence of water and corrosion.
If there is you will need to replace the computer. You will also need to take the computer apart and seal the new computer with silicone to prevent it from re occurring again.
Right click copy and past this to a word document and take it to your mechanic.
Let me know if you have further questions.
If not please hit the green accept button so I may get credit thanks.