PhD supervisor making me do a LOT of non PhD work
Although there may be a number of people here who are quick to claim that no PhD advisor would ever take advantage of the cheap and free labor that PhD students can be coerced into (by means of using degree and thesis requirements as a figurative cudgel), I think that it is somewhat common that PhD advisors make use of such free labor. This should not be. 

This being said, there are a few things to consider:


The grant application you are assisting in might be a direct means of funding your future research. That is the "pay off" for you. Nothing happens in academia for free. Make sure that you are being compensated, but also keep in mind that not all compensation is directly and immediately monetary. 
A few months of weekend work is sometimes part of "paying your dues" in academia and can open up further opportunities for you. (Such as a future post-doc with this professor). 
Address your concerns as to timeline with your supervisor. If she dismisses your thoughts entirely, you may want to consider if this is really a professor you want to do a post-doc with.