We assess the validity of assumptions that underpin common low-dimensional rate theory descriptions of nanoscale stick-slip friction by completely specifying harmonic transition state theory kinetic parameters from an atomistic model. The resultant kinetic model is able to reliably reproduce the temperature and velocity dependence of friction as obtained by direct fully atomistic accelerated molecular-dynamics simulations. Analysis of the parameters extracted from the model indicates that, while energetics of the transition pathways can be adequately captured by low-dimensional effective Hamiltonians, rate theory prefactors contain inherently high-dimensional entropic contributions that cannot be accounted for. Despite these limitations, we show that simplified models can still be sufficiently robust to capture the prominent features of stick-slip friction.