Ambien can do this especially to older people (not sure of your mom's age). So can other drugs. Iv'e seen it first hand. Your mom may be dwelling on it because she thinks she is going "crazy" when the fact is the "crazy" was a result of a reaction to medication -- and is NOT any actual mental illness on her part. She needs to see a doctor who can reassure her of that strongly and who will examine her physically and emotionally and run any tests needed to see if the medications (including any she is still taking!) are still affecting her.
Please know this: Once a woman is over "a certain age," many, many doctors and other health professionals treat them -- eventually, us -- like dumb children. I've seen doctors tell my late mom and many of her friends as they got older that whatever they were going through (from mental issues to COPD to, yes, cancer) were initially "just the changes of age" or "you're post-menopausal and these things happen." Seriously. Doctors didn't want to spend time with these older women to find out if they were really physically ill; the doctors just chalked everything up to "they're getting old, it's post-menopausal, it's in their heads" etc. So you MUST be a strong advocate for your mom with doctors. You and your sister should see her doctor IN PERSON and though he or she will say "I can't discuss a patient even if she's your mom," YOU can still talk to HIM. Dont' let anyone dismiss your mom or try telling you "it's all in her head." If it's the medications and she's upset they need to deal with it. Don't take no for an answer.