I recently acquired a kitten and was wondering if either or both of my
houseplants are a danger to her. I have an Aglaomena modestum and Dracaena
marginata.

I don't believe so. Dieffenbachia is poisonous. However, you don't want her
messing in your plants anyway. Cats like some fresh greens in their diet, and
you are a good cat owner & will not allow her outdoors. The way to keep her out
of your houseplants is to give her her own grass pot. The pet stores sell grass
seed specifically for this purpose.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)