MIL uses car too much

so my boyfriend’s mom asks to use mycar because hers needs work done and is just sitting in their drive way for now, she’s been using ours here and there to go pay bills and such, but lately she’s been abusing her privilege by calling all day long like every 15 mins bugging to use the car. my tire’s are in really bad shape ( right back one is flat ) and she uses my car to drive to a city 45 mins away to run errands when she can do all of it here in our city. i tell my SO that i dont want her driving on the freeway to the next city over because of the tires and he still lets her, completely ignoring me. am i wrong to be mad about her using the car too much ?