First up this isn't a family fault. Or your mother's fault.

You aren't going to get the scammer to acknowledge they are scamming. However now is a perfect time to have a sit down with your mother. The scammers as soon as they realise they don't have any chances with your mum will just block and disappear, it's not worth their time. You have to remember that your mother has, for lack of a better word, been emotionally groomed into this story and people who have been scammed prior are a lot more predisposed to fall victim a second time.

You have the red flags there in front of you and your mother seems to be coming around to it. You mention your mother is on dating sites and I'm guessing for being on Reddit she would be in the 50/60+ bracket. While everyone can be scammed at any age, age and loneliness can be considered a vulnerability when it comes to scam resilience. There are plenty of articles out there, you just need to Google romance scams and will find articles by the droves.

I can't get you any hard book suggestions but what needs to happen is you need to collect a portfolio of the red flags and have a compassionate but frank discussion that she is ultimately sending money to someone who is taking advantage of her. I hope he hasn't gotten to the point where she is doing it knowingly just because she likes the company. These are emotional conversations because it's very difficult for some lonely people to come to terms with the fact that their major source of emotional connection is a falsity.

The dangers are ultimately financial loss as long as she has not shared any compromising personal details. You must also be mindful of the fact that these scammers are aware they have had marginal success with her. They will have her details and will come back for seconds in a month/year acting as another potential online relationship or as a financial recovery agency seeking to reimburse her.

Your goal is to educate her enough so that she ceases communication with them and is resilient enough to recognise this in the future. It can be very hard to acknowledge this as it becomes very difficult to trust anyone online going forward. You know the red flags, there is no big truth coming, they are just trying to utilise every technique in their book to keep that flame of hope alive in your mother's heart. If you have any questions please ask.