Your daughter got an undivided 1/3 interest in the property and she paid nothing. If she's personally obligated on the mortgage and you're paying it then that's part of the gift as well. So, the gift would be 1/3 of the $200k down payment plus her share of the mortgage that you are paying.
Another person in this thread is confused.....this is not the same as, say, a joint bank account where one person deposits all of the funds and there is no gift until the other joint owner withdraws some or all of the funds in the account. Your daughter has 1/3 ownership which is irrevocable since she's on title and that has value immediately.
