I would actually like to address a couple of things here. First of all, your daughter’s patent foramen ovale (PFO) had nothing to do with her prematurity. All babies have a PFO in utero—it’s supposed to be there. That is closed by age 1 year is also normal. It typically has no other effects on the heart.
More importantly, though, is your daughter’s symptoms. I don’t have all the information about her tachycardia in front of me, so I don’t know if she is having sinus tachycardia or supraventricular tachycardia, the latter of which is an abnormal fast heart beat. I’m not sure what vaso-vascular disorder is; are you sure it’s not vasovagal, which would be a form of syncope, or passing out? I can’t say for sure, but her mastocytosis certainly could be the cause of her symptoms. The chemicals in the granules in the mastocytes can cause the blood pressure to drop, which then causes the heart rate to go up and can cause many of the symptoms that you are describing. Typically, besides using antihistamines to block some of the systemic reactions from the degranulation, your doctor may need to consider other medications to block the response, such as beta blockers. You should speak with your doctor further about what is happening in mastocytosis and what medical interventions can be performed to control the symptoms.