Grandma scammed by former student claiming homelessness

I love my grandmother; she’s a very generous person, though very vulnerable to scams and she’s getting old. To start, she was a teacher to this student who claims he watched both his parents pass, which has left him with troubles and he’s apparently “homeless” and struggling. He asked my grandma for money one time as an “emergency” and kept asking from there. She probably gives him at least over $20 a week from what she’d let me look at. He also has been asking for money for random things without labeling what he’s buying or who the money is going to, because he asks for money for his girlfriend and “friends” who are stranded, which leads me to think he may have a home and be using my grandmother as extra income to supply his drug addiction. He also is obsessed and needs the money within 5-10 minutes or he sends my grandma 10+ messages and spam calls her within 3 minutes… I just feel horrible for my grandma because she has cancer and is crippled, and she has also been exploited her whole life by her ex-husband, the father of her three children (aka my dad and aunts), and she doesn’t fully understand he’s using it for bad things and not actually using it for food or rehabilitation back into a normal life. He just uses his trauma on my grandma and it works because she feels like she needs to give him money because he watched his own parents die.. I'm sorry for the long message, I'm just fired up because my grandma doesn’t see it’s a scam yet, and my mom didn’t see all the messages I saw between him and my grandma. Thank you for reading, any help is greatly appreciated. I want to protect my grandma as best I can.