If she insists that you all set this goal together, perhaps it is time to tactfdully point out to her that she is not keeping up her end of the bargain. Not having enough time might equate with lack of inclination and lack of energy due to lack of exercise. You might also point out to her gently that it is not the amount of time you train but the quality of training you do in the amount of time you have.
Ultimately though it is you can only be responsible for your health and fitness goals, just as she needs to be responsible for her own.
It's a hard narrow line to walk though, good luck with that.