I think UCLA would be a good place to seek help for your mom. Both of these pages show Meralgia Paresthetica in their lists. I wasn't able to find any references for Meralgia Paresthetica and UCI.

Diagnoses - Peripheral Nerve: https://www.uclahealth.org/neurosurgery/diagnoses-peripheral-nerve
Meralgia Paresthetica: https://www.uclahealth.org/neurosurgery/meralgia-paresthetica

You might just want to give them a call and discuss your mom's symptoms and see if you can setup an appointment for her - https://www.uclahealth.org/neurosurgery/contact-us

Mayo Clinic Network does have a location in Southern California but I'm not sure if they have any services related to Meralgia Paresthetica or neurology. Here's a page that talks about Palomar Health. It might be worth calling them as I believe Mayo Clinic affiliates have access to Mayo Clinic resources and doctors for collaboration.

-- https://newsnetwork.mayoclinic.org/discussion/first-california-member-of-the-mayo-clinic-care-network/
-- https://www.palomarhealth.org/

My primary care diagnosed me with meralgia paresthetica - at first it was extremely painful. I was told to make an appt with an orthopedic doctor since my xrays also showed hip arthritis. Because I was in so much pain and could not get an appt for weeks, I decided to try a chiropractor. Research on the web showed that neuro chiropractors were successful at treating this. I found one (specializes in treating nerve pain) and went last week. She used ultrasound and that night I had my first sleep without pain. Since then I have mild pain off and on, she said it would take a few visits. You definitely want to get a medical diagnosis of course, but its something to consider to help with the pain.