Hey man, I'm going through the exact same thing and totally understand where you're coming from. I'm super frugal and consider myself good with money as well. I've worked super hard to get to where I am in life, but my mom spends like no tomorrow and I recently found out she blew $100,000 at the casino from gambling.
Worst of all, a few years ago, I helped her get a mortgage for her house using my name so we have a joint bank account/mortgage together, so she's been taking LINE OF CREDITS from that account to gamble at slot machines. Since it's a joint account, her $100k line of credit borrowing fell under my name as well (I had trusted her with the joint account and never looked at it) until one day I see that my CreditKarma fell to 600's (it's usually in 800's, I pay off my cards immediately). It fucking ruined my life. I was SO mad.
Let me tell you now, I know it hurts and you want to help because she's your mom. But you can't anymore, and what everybody said below is true. You have to cut her off. This isn't some internet generic advice. I actually went to talk to financial advisors, family counselling, and psychiatrists about this. It was not fun.
When we went, the family counselor/psychiatrists told me the one thing I did not want to hear, and that is, my mom has a gambling addiction. Everytime the counselor talked about anything else other than money, my mom reacted annoyed/frustrated that she had to be sitting there like she had a problem, but everytime the counsellor asked her about her winnings, my mom started to speak enthusiastically and smile and was excited to share her story about winnings. It was a clear sign of addiction.
The ultimate advice was that we had to cut her off. Unfortunately there is nothing we can do. This was hard for me to accept, but he told me the only way for gambling addicts to get out of this is when they feel that they have reached rock bottom themselves. Only then, hopefully, they realize this themselves and stop gambling.
So, like others have said on here, and through my own personal experience. You have to cut her off financially and she needs to feel the pain herself. There are also gambling resources where she can choose to self-ban herself from casinos (they're not enforced well at all). But maybe it's something you can look into anyway.
Really hope this helps. Good luck. It's not going to be easy and sorry we have to go through this.