You may wish to focus on helping her address the underlying anxiety, rather than on removing the digestive symptoms of anxiety. When children have unhelpful thinking which may then impact their physical health, some parents find Cognitive Behavioral Therapy (CBT) to be helpful.

You may have read this elsewhere on the forums: Possibly this scientific explanation may help her: its from the book, Make Your Worrier a Warrior, (2013, Great Potential Press) authored by Daniel Peters Ph.D. who lends expert insight to understanding what a child may be experiencing. For example, pages 44-45 suggest that parents may wish to think of acting out as
Originally Posted by book, Make Your Worrier a Warrior
a variation of the "fight or flight" response... children couldn't articulate their fears... they were reacting behaviorally because their amygdala, or their emotional brain, was overriding their thinking brain... kids often do not have the emotional vocabulary and/or insight to tell you what is going on...
Armed with this knowledge, working on helping a child understand nuances of feelings and vocabulary to express their interpretation of what they are experiencing, may prove helpful.

If anxiety is related to perfectionism, procrastination, and/or reluctance to try new things, some of the resources listed in this old post may be of interest.