What you don't say is if she is thinking anxious thoughts and obsesses over irrational fears. That's what anxiety is. It isn't just physiological symptoms. So is your daughter thinking anxious thoughts, is she severely afraid of things she wasn't before and others aren't? If not, it's probably not anxiety and your doctors just haven't looked hard enough yet to find the answer. You also don't mention if she's getting severe headaches -- if she was I'd say she's suffering from migraines. But it could be so many things that a physical by your average general doc won't find -- thyroid, for example, is almost never checked correctly by your average doc if you don't ask them to -- they don't check the right measures. Nutritional deficiencies are hard to pick up because some people, although they fall within a range, might still be on the low end and it might affect them more than it does others, assuming the docs even know how to check for them or bother to check for them. It could be a hormonal thing, especially given her age. It could be blood sugar imbalances that won't show up on your average blood test but might with a more comprehensive glucose tolerance test. There are hidden viruses that are very hard to find. Nobody on here can tell you what's going on, but again, is she feeling anxious and severely fearful to the extent it could cause such a severe reaction? One thing about them that does suggest anxiety is that you say they happen once per week. Is it the same day every week? That might suggest a trigger that something has happened in her life that is making her severely anxious because it's at a time of the week she has to face the same thing. These are the things you need to know before labeling it an anxiety problem. If you decide it's not anxiety, then it may be you need better doctors who do a more thorough job than your average overworked general doc. If you decide it is anxiety, therapy might be needed quickly. Sound her out about what's really going on with her thinking, because anxiety is a disease of thought.
I am not meaning to generalize, however it is common for many anxiety sufferers to believe something is physically wrong when it isn't - so that is the likelihood after a few doctors said the same thing.
Has she gone to therapy to see if something else if making her anxious, or if there is something she can do to calm down? How does she calm down or are the attacks short?