If it were mine I'd fix it. But, you do need to know the extent of any undercarrriage damage; straightening can be expensive. Also, did the motor mounts break in the accident? If you had comprehensive insurace, this makes a huge difference. I'd pull the grill/bumper and quarter panel before making a decision. I'm glad your daughter came out of it okay. This may be an indication of the toughness of your MB. I was in something like this in a Chev S-10, which drove the engine into the passenger compartment and me through the windshield.