It is always going to be different loving a girl who has anxiety. You are not always going to go out and do things on the weekends: you are going to have nights where you sit there and comfort her from panic attacks that she does not know the cause of. You are going to have times where you probably will get frustrated and overwhelmed by the fact that you cannot do anything to help her. It is a really difficult position to be in sometimes, but there are a few things you need to know about her when you are in this relationship.
Patience is so important. The most important part of helping her is telling her to breathe, which she sometimes forgets how to do. It is going to feel like her chest is closing up and she will not know how to stop it from happening, but your patience will help her calm down. Her breathing will go back to normal and within a few minutes she will hopefully be able to go back to her normal everyday self and move on with what she was doing. You probably will not realize how important it is to her or how much it means to her when you can sit there and be patient with what is happening. It feels like she has someone who in some way can understand how she is feeling and she has someone who can help her when she is experiencing this mental pain.
You will never stop hearing the word sorry, ever. She will most likely feel like she is being a burden because of how often she needs you to comfort her. You never feel like she is but no matter how many times you tell her to stop apologizing for this, she never will because she will still feel bad. Do your best to try and convince her otherwise. It could potentially help her to relieve some of the anxiety that she is feeling because you have made her feel more comfortable in that moment of panic. This is going to be really difficult sometimes. You probably will not understand why she does not believe you even though you have said it in as many ways as possible. Just do your best. One day she will realize you are telling the truth.
You really only have one job in this situation, to tell her she is going to be okay. You can not fight this battle for her. It unfortunately is something that only goes on inside of her head and can not be fixed just by telling her to calm down. But, telling her she is going to be okay is going to reassure her that you are there for her when she needs you. It is an everyday battle suffering with anxiety, but I promise you that you will make a difference in her life by being that support for her whenever she needs it.