In Platinum, when will I be able to battle Dawn with her starter at it's 3rd evolution?

Question

Because I need the Torterra to at least be seen so I can finish the local Pokedex.

Answer 1

There will be one in Victory Road so you can see it there. Torterra is used by a female Ace Trainer named Sydney on floor 2F.

Source

Answer 2

You never battle your friend (Dawn) in D/P/Pt. You will only battle with her (I don't know when). Also, her starter never reaches the final evolution (I'm not sure).