I'm sorry but I must say that suing the Vendor for that is
not too different from buying a car, learning that it has a broken brake in your garage,
then you drive anyways and get into a collision(accidents are when you just get unlucky) and blaming your dealer.

I would be just glad that 10 years old daughter isn't hurt.

I respect that you are hurt, and ver upset that this all happened
because either the vendor sent you the transmitter broken, or it got broken from shipping.

but you did mention that it was you, who plugged it into the computer and learn that the throttle doesn't work.
and you saw right out of the box that '3D switch' was broken off.
(I would understand if you are a beginner, because I almost created a mess with my first helicopter, just for wondering what "Idle up" meant)

If you still think that was someone else's fault even after, you think over all these.
and you wish to bring up the law-suit to the vendor

I have only one more thing to say...
I'm sorry