Start by casually asking if she needs help with anything -- perhaps a financial task that she really doesn't like doing. For example, you could say something like, "Mom, I was wondering if you use automatic bill pay. I've found that it makes my life so much easier because I don't have to worry about writing checks and mailing in payments. If you'd like, I can help you set up automatic payments for your bills."
You also could have a conversation with her about scams. Tell her about a scam call you got or a scam you've heard about. You could talk about how convincing scammers can be then suggest that she use a service such as Carefull to help monitor her accounts for unusual transactions and signs of fraud. The goal is to offer your help (and services to help her stay on top of her finances) rather than to simply suggest that you need to be involved in her finances because she might be making mistakes. You don't want to highlight her shortcomings because she might become defensive and push you away.
Try these approaches and let us know if they work. If not, we'll help you brainstorm other ideas.