99 grand prix 3.8 v6

It has around 150,000 miles, and the rear shocks went bad and the drivers side trailing arm broke all at once. I had an alignment done about 2 minths before this happened.
I replaced the shocks with brand new shocks , mounts pads and all but some ****ty looking trailing arm that was off a 2000 grand Prix. The arm had surface rust and was the stock U shaped design. After everything was put together we drove it around the block one time and the replacement arm is already bent!!!

Do i just need a better trailing arm, or is something else probably wrong???