How much should Papillons exercise?

I just got a three year old Papillon, and she seems to really enjoy running with me. So far, we are doing something like 5 miles per day together, but my landlady just told me that I shouldn't let her do that, because it might overheat her or burst her heart, because Papillons "aren't made for much exercise." I'm not sure what to do. I don't want her to get bored being inside a lot, and she certainly seems to like running with me, but I also don't want to hurt her or anything. Does anyone know how much exercise is safe for a small dog like that?