Ceteris paribus, you can calculate the time that it takes your and your sister's respective vehicles to cover any particular distance based on the cumulative differences in your relative rates of acceleration over the time/distance interval involved.
This rate of acceleration at any particular moment is primarily a function of the amount of torque that is applied to the particular mass (i.e., weight) involved over the particular time/distance being "measured". However, the rate of acceleration is also substantially affected by the relative differences in "gearing" involved. For example, it's MUCH easier to start a bicycle from a dead stop in a lower gear than it is to start that same bicycle from a dead stop in a much higher gear even if substantially more HP/torque are applied. This will not be true IF and ONLY if the amount of HP/torque (read "force") that is applied to that higher geared bicycle sufficiently exceeds that being applied to the lower geared bicycle that the higher geared bicycle's rate of acceleration exceeds that of its "competitor".
Stated somewhat differently, regardless of any weight differential that may exist initially, there is a statistically valid and reliable basis that you will prevail in your prospective sibling rivalry-based event (i.e., kick your sister's M3 driving butt in the quarter mile) if the cumulative rates of acceleration of your vehicle exceed that of your sister's vehicle over the distance involved. Again, this will be determined in part by the sheer amount of "force" (determined by the HP/torque measured AT the rear wheels) that can be applied as a function of time. however, bear in mind that the amount of HP/torque (read "force") that is actually being applied at any particular moment in time (and, more importantly, CUMULATIVELY for the time period/distance involved) for the ultimate outcome of your event (i.e., the rate of acceleration over time) is very subtantially impacted by the relative differences in the gearing used by you and your sister in your respective vehicles over the time interval(s)/distance involved.
Put a little more simply, if you or your sister don't maximize your available "force" at each time increment/distance through a judicious useage of your gears/RPMs for that gear then you will lose even if one or the other of you otherwise had a competitive advantage initially (either because of differences in the weight/"instant" force available gearing to apply that force in your respective vehicles).