My girlfriend says her dad asked her to let him touch her sexually "just to get it out of his system"

Throwaway because I'm concerned for my girlfriend's family's confidentiality<br><br>I'm 22M, she's 21F. We've been together for 2 years. Things have been absolutely great in our relationship. One day earlier this week (maybe Tuesday) she came to me with tears in her eyes and told me that she needed my help because something absolutely horrific had happened to her. She told me that she went to help her dad set up a party at their house for the weekend, and that he got her alone and told her that he was going to ask her a question, and that she needed to promise that she wouldn't get upset or angry. She said obviously, she was a little apprehensive, but when he said that she agreed because she trusted him. He asked her if she had had sex yet, and she told him that her and I have been sexually active for almost a year. <br><br>She said he paused for a minute, looking at the floor. He then looked her in the eye and said that he was going to ask her another question, and that he needed her to again promise not to react poorly. She said she had no idea what was about to happen, so she says she agreed again. Her dad then asked her to let him touch her vagina, just one time, and only for a moment, because he had always had sexual feelings for her and wanted to "get it out of his system" so he could move past those repulsive feelings. She said she was horrified, and she got angry and yelled at him, telling him to get off of her. <br><br>She said he apologized profusely and acted like he didn't know where that came from or what he was thinking, but that he just can't stop thinking about her sexually. He was making up all kinds of excuses like how he thinks her mother is having an affair and that's why he's been insecure and started thinking about her. She told me that she left immediately, and that he texted her an apology and offered to get her into therapy to help her with her trauma. She's an absolute mess right now, and I'm kind of at a loss for what to do. <br><br>I told her that I think the next time he reaches out, she should ask for a call and that I would "listen in" while she talks to him. Then she can put me on speaker and we can both tell him off. She's not comfortable with that though. What should I push her to do? How can I help her with this, and how can I make her dad suffer for putting her through this?