My mom is about to have epidural steroid injections in her back for bulging discs. What are the side effects?

Usually minimal if. If given in the proper setting, minimal unless diabetic (elevate blood sugars) or have been on steroids chronically affecting horomonal balance. Local soreness or flush sensation/redness of skin can occur. Rarely, aseptic necrosis of bone can occur. A possible spinal headache or aseptic or chemical meningitis. Local soreness at the injection site is transient. Rarely, nerve or cord injury.
Generally safe. Epidural steroid injections are generally very safe. Some possible side effects/complications include headache, bleeding, infection, nerve damage, and allergic reactions. You may also experience side effects related to the steroid medication, including weight gain and hyperglycemia and well as transient mood and sleep disturbance.
Until recently. Very few and infrequent but now we can add death as a possibility if the pt is elderly, debilitated and the drug used is from a compounding company in massachusetts. Frankly the risk and side effects are small and ask the proceduralist where the steroid is from. Most pain docs get the drugs from major pharmaceutical companies.
Very little. When an epidural steroid injection is done by someone with a lot of experience there is very little chance of side effects. Like any injection, you can have pain at the injection site. Ice is helpful for this. There is also the rare possibility of infection, cerebrospinal fluid leak, and bleeding. All should be addressed by a physician as soon as possible.
Epidural Steroids. Current problem of steroid epidural injections is focused on contaminated steroids that can cause fatal fungal meningitis. Discuss this matter with your pain control doctor.