Sorry to hear of your loved one tearing her Miniscus. I tore both of mine (inside and outside part of the knee) on my right knee a few years ago. Not sure but I think they call it interior and lateral miniscus. Was off work for a month. Hope everything goes well for you and you get things sorted out.
Yup, unfortunately it will happen that way. The operated on knee will be imobile for a bit and be sore which puts strain on the opposite side accenerating degenerative changes. Also any type of bone injury tends to trigger osteo-arthritis so whammy #3. Depending on how much cartilage is removed you may require "Rooster-Comb" injections into the joint every 6-mo or so at $600 a shot. We won't even mention knee replacement