Actually a mutual friend of her told her about this guy, that he is a nice person and so on. She belived the guy being friends, and he started to talk with the other guy about coinbase and so on. He asked her to install an app in her phone , so he could help her out with her account, he initially told her that he works for some king of blockchain agency in luxembourg...
Is this mutual friend an online friend or can you meet them? If it is the latter can't you try locating him and ask him about his friend? It is really unfortunate but it sounds like your mom's friend is also on this if he says that the scammer is a nice person and so on. If it is an online friend, I'd suggest educating your mom about better security practices. From the way you describe it, your mom seems to be unaware of the common scam tactics and how to protect ourselves against them.