How to comfort someone?

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My girlfriend lost her dog recently and she cried rivers because of that. After some weeks, she's moved on and is happier than ever carrying the memory and the connection she had with her dog. Last night, she had a terrible dream about her dog and she saw it dying once again in her arms and what's worse is that she feels that it's her fault. She recently called me early in the morning crying about it and telling me the details of her awful dream but I just cannot know how I can comfort her... I told her that I'm with her and just listened to her. I comforted her that it's just a dream and it's not real, but still, I don't feel like I have comforted her enough. Eventually, I just told her to sleep more, and feel everything she feels, and that I love her so much. I am sure that many of you here have lost a beloved pet and I am seeking wisdom on how to comfort a loved one that lost one. Thank you for your responses.