We live in an apartment on the third floor. (I hate supply delivery day)
Sometimes dh runs late into the night. Never had a complaint from any of our neighbors, but the downstairs family is much nosier than us!
I would compare the noise to having a fan running, constant hum of vibration, irritating if you are a light sleeper I guess.
Hopefully your neighbor will find some understanding when she realizes it's not like you have a choice. Maybe offer to buy her a fan to run to drown out the noise? Good luck! We dealt with a crabby neighbor downstairs that insisted on propping all the fire doors open.. complaining of "smells".. well gee, I complain that I don't want to die in a fire and we pull out the door stoppers.
Our owner finally put in emergency auto closer doors.