What could Terry get?

Second degree.

She didn't plan the murder, so first degree is out.

But she knew a woman was in the trunk of the car and sent it into the water any way. Second degree murder is a non-premeditated murder from the result of an assault where the death of the victim was a distinct possibility. That fits in with Rosie's method of death.

Now whether they struck a deal with her or not, who knows.

She should have received a fast trip to meet her maker.

It actually would be first degree homicide. As long as she intended to commit the homicide, it doesn't matter if that intent was formed two weeks, two days or two minutes before acting on it. She knew there was a girl alive in the trunk and knew that driving the car into the lake would cause her death. That's first degree.

SPOILERS///

it's been a while since i've seen the 1st episode. did she know for sure that the girl in the trunk was still alive or was she was just trying to dispose of the body? if it's the latter, then it would not be 1st degree murder.