The Defenders will debut in 2017, and Marvel has not confirmed a release date for the second season of Jessica Jones.
If Rachael Taylor’s training is for the second season of Jessica Jones, then she’s getting a serious head start on the fitness regimen; chronologically The Defenders would make more sense.
The general rationale for this assumption seems to stem from the fact that the second season of Jessica Jones won’t premiere until well after Luke Cage, or Iron Fist, or even The Defenders have all finally debuted.
At this point it remains unclear whether or not Hellcat will debut when The Defenders finally premieres.