My sister went with oxygen for 7 minutes and a heart attack she a diabetic and had very low blood pressure kidney damage will she have brain damage?

Not sure. Adults who are deprived of oxygen due to cardiac arrest for over 5 minutes usually suffer brain damage. However since she did not have a cardiac arrest and,despite very low blood pressure, she may have had enough cerebral circulation to avoid significant brain damage. However because of diabetes and smoking history, she may have come vascular disease which increases her risk. Hope for the best.
Here are some ... I assumed you meant "... without oxygen for 7 minutes ...". The insult to all tissues and organs under the described clinical scenario is bound to happen, but just a matter at what degree, which will manifest over time. Now, how to keep up a free-flowing circulation to nourish all temporarily O2-/nutrition-deprived tissues / organs is the key personal & professional task - yet, the only best hope.
7 minutes is a while. Was she found down and it was 7 minutes before any CPR was started along with respiratory support or was CPR started right away but it took 7 minutes to get an airway on her? The target time limit for before brain damage occurs is taken to be 4 minutes. Having said that everybody is different and therefore, if your sister is in a coma right now we must let 24 hrs. elapse before saying much more.