To say that she isn't running in February implies that she's not running during the upcoming February. To say that she does not run in February implies that she does not run during February at all - the upcoming one nor any other in her lifetime.
because all the sentence are in present .. indicativo serach in one world italian https://www.youtube.com/channel/UCVGo10hbyIyD6cbz3Jm3aoQ
Because " doesn't run" refers to habitual action. "My grandmother isn't running" is either now, at the moment or an arrangement (plan) in near future. For example: "I go jogging on Fridays"(every Friday) but "I am going jogging on Friday"(this Friday).
Why won't Duolingo accept granny for nonna? In Britain it is a very common along with nan!