'Teen Mom' Mackenzie McKee -- Rattled By Crash ... But Rollin' With New Shake Deal

Ex "Teen Mom" and "16 and Pregnant" star Mackenzie McKee got a case of the shakes -- the good kind that'll help her cover expensive repairs on the SUV she drove into a ditch.

A source close to the situation says McKee is one of the best promoters for 310 Shakes -- and when the company got wind of her accident ... it stepped up with $10,500 she needed to help fix her ride.

TMZ broke the story ... Mackenzie said her diabetes caused her to zone out and drive her new and uninsured Kia off the road.

We're told the cash came without strings ... 310 just told her to keep up the good work -- a reference to her promoting skills. Not so much her driving.