I have a few suggestions, depending on your financial resources and location. These are based on my experience as an occupational therapist as well as my own personal experience living with pretty significant SPD:

1) Consider consulting with an occupational therapist. It may be hard to find someone who works with adults (as most SPD-focused OTs work with children), but they will be able to provide the most individually tailored support for your mother.

2) Look into the possibility of Irlen Syndrome (http://irlen.com), which is caused by difficulties processing visual information in the brain and can result in severe sensitivity to light (as well as other issues that may not seem obviously connected). Irlen Syndrome is addressed by wearing special tinted glasses and/or using colored plastic overlays (on books, computer screens, etc.) to filter out particular light wavelengths. The website includes several self-administered tests.

3) Sharon Heller's book "Too Loud, Too Bright, Too Fast, Too Tight: What to Do If You Are Sensory Defensive in an Overstimulating World" is a great resource for explaining sensory defensiveness and providing guidelines/exercises for addressing its effects. For example, your mother should try to ensure her living/working environments are as calming as possible, which may involve dimmer lighting, blackout curtains, removing visual clutter, etc. Even simple things like facing away from windows (light and glare) can really help, but simply may not occur to your mother because she's just gotten used to dealing with it.

4) Encourage your mother to be physically active. This could be going for walks, gardening, swimming, aerobics, playing with grandkids--anything she enjoys! Getting enough physical activity is really important for regulating the sensory system. On that note, making sure she gets enough sleep/rest and good nutrition are also really important. (I know that's pretty cliche advice, but it's really so, so important for those of us with SPD!)

5) Things I have found personally helpful for my own light and sound sensitivity: earplugs (experiment with different kinds; I prefer reusable silicone ones instead of foam); listening to headphones with soothing music (especially helpful in busy, crowded places like grocery stores); sunglasses; hats with brims; and using meditation/mindfulness exercises when I'm feeling overwhelmed.