Honestly, as someone who has had friends repeatedly get into bad relationships, it’s supper frustrating to watch and can absolutely get exhausting. You have to be patient with them but also call them out when they are repeating the same harmful behaviors. She should definitely get into therapy and stop seeing this current guy, but I think if you like her it would be a good idea to make it clear to her that you are interested.
Part of the reason she might be going with the toxic guys is because they aren’t thinking about how long to wait before making a move and she needs to feel pursued and loved when she’s getting over heartbreak, it’s not a great coping mechanism so you might want to talk to her about it.