Wrong Number

While taking a nap today, a phone call woke me up. I had called someone earlier in the day, so I thought it was probably them, until I looked at the number, and I realized it wasn’t.
"Hello?" I answered.
"GiGeeGee?" she asked.  I almost sighed.  I was trying to think of a way to tell her to stop calling that would actually work, because I've told her to stop calling for ages now and she still is doing this.  As I paused, she apologized and hung up. 
About a month ago, this woman began calling me. She always sounds confused, and I’ve explained to her (she’s called at least ten times) that I don’t know who she is.  I suspect she's an older woman with memory problems, because no amount of "stop calling this number" has worked so far. 
Last week she called me twice while I was at work, which makes me nervous. Most of the time people at work are cool, but what if I’m in a meeting? What if she does what she did last week, where she called me in quick succession?
So I just sent an email to my Mother asking how I can best block her phone number. Mostly, I want her to know what is happening since we’re on a family plan and someone calls her asking if she knows I've had to block someone's number I don't want her flipping out. 
I was reluctant to take any action until now because I was hoping this woman would stop calling or someone was taking care of her and make her stop.