If you transfer to yourself, you will have to pay donations tax (about 20%) but you can also be held liable for theft (ie transferring it from her).
My parents invested with Alan Gray, it pays interest out to them monthly, same with some fixed deposits. The interest can be paid into a seperate account which she can use, but the principal remains. Just check the penalties, in case she needs to access it immediately. You may get lower interest, but incase she needs the money for hospitals.
For you to manage it, you would need her to sign a power of attorney.
Best bet. Go chat to a financial advisor (Old Mutual has some good ones), or chat to Alan Gray. You could also chat to her bank about what they offer. And then you and her must go to an attorney to create a power of attorney (safe is she is unable to, or get alzheimers etc). She can also draft her will at the same time. You musnt sign the will as witness, otherwise it would invalidate it.
Hope this help. We had to go through the same process for my mom and dad (my dad had Alzheimers).
Stanlib is good, and some shares also could be beneficial depending on her exposure.