You could make the dough ahead of time and carry it in a cooler. When everyone asks about cookies, AH-HA! you have the cookie dough ready to color and shape. NO MESS in mom's kitchen (not that it sounds like that is the main issue, just one less thing for her to focus on). In fact, I would almost take everything....cookie sheets, supplies including coloring and frosting, plastic wrap, parchment paper, etc... make the clean up as easy as possible ($1 store bowls that you could throw away, no washing ANYTHING). Mostly just to make the only thing that you use is the oven. put everything in a tote to transport.
In the OP you stated that you did this as a tradition with your dad, could this be why she isn't wanting to do it any longer? it isn't HER tradition, does it make her sad? or mad? Or is this just kind of status pro quo for her?
{{{hugs}}} for you whatever the reason. This has to be hard.