As seancornelis says the 190D is one of Mercedes Benz's mainstream models and a very reliable unit from new. Even today they still make for safe, dependable, economical transport but like every other make and model of car it's the condition and the upkeep that determine how you'll go, along with driver abuse
Perhaps it's plain worn out (how many miles on it again?) or your mechanic is unfamiliar with it, incompetent or just a plain greedy rip-off - setting your Mom up for a series of costly repairs?
Perhaps because it's your first car you are the incompetent factor here, and would destroy any vehicle you get your hands on .. be it a Mercedes, Buick or a Sherman tank
I have a Merc, look after it, and it goes great - a pleasure to own and drive. Conversely, my uncle had a dreadful run out of his one, caused by the false economy of taking it to a cheap, shoddy mechanic who was more suited to working on clapped-out taxis.
Why not get a second INDEPENDANT opinion and quote, from either your motoring organisation or a different reputable mechanic, preferably a Merc specialist, as to your 190D's condition and what future repairs are required?