A Toyota will most certainly cost you less in upkeep. They are both good choices, but I'd go with Toyota/Honda for my daughter. The Benz's are great cars, but there will be service issues that come up--and these issues will be expen$ive.
On your mileage longevity question, my '91 300E has 192K and runs perfect. These cars last a VERY long time with proper care.
Besides, if she buys a Benz-there will be one less for me
-GH