Death at Sunset Marilissa question?

Im trying to tie up my research for my first module tmrw of Dragon Delves, and Im realizing for the Death at Sunset adventure, how do u keep marilissa from joining the fight against the green wyrmling? if u encounter her first, u can lie and escape her at the moment, but it specifically says" if she notices the chars fighting any other lair denizens, marilissa enters the fray against them." if u say ur here for the dragon, u end up fighting her. since the fight against sunset is nigh is in this cave, and pretty close to her chambers, its pretty likely that she would notice. not even mentioning that she is a cr 3 yuan ti malison type 1