She should find out from her doctor exactly what types of light cause a problem for her. For some people, it might be a bright light in an otherwise dark room and for many the biggest problem is a pulsating light or strobe light. WDW does try to avoid those types of lights in the attractions or limits how long the light is on.
Here are some links to past threads about epilepsy at WDW from past threads:
Epilepsy at WDW. This one has a lot of specific information including rides with lights. The ride listing is on page 2
Stobe Lights and Epilepsy. This is more general about epilepsy (a parent asking questions about epilepsy).
My youngest DD has epilepsy and usually has a least one seizure on each of our WDW trips.
The only light that bothers her is a sort of pulsating light at
Maestrom in Norway. She is very uncomfortable in that area nd covers her eyes. My mother, who gets migranes, also said that light bothered her, although she did not get a migrane from it.
She has not been on Space Mountain (I haven't either in many years) so I don't know about that light. She has been on all the rides listed in these 2 threads repeatedly over the years and has never had a seizure associated with the lights.
Dehydration, lack of sleep and change of medication schedule (hard to keep track of time when you are having fun) are much bigger seizure triggers for most people at WDW thatn the lights are. All of those things can lower the seizure threshold (how much stimulation it takes to begin a seizure), so controlling those factors will help a lot to avoid seizures.
