I respond mostly to keep your post on the top of the list.
I don't know what an "inferior ischemia" is and have not tried yet to look it up. If you have more information, other input from the doctor and wish to share, that may help us to better explore your questions.
Inferior ischemia is not a rhythm. It is a change in the heart. Ischemia is basically when anything is not getting enough oxygen, enough so that it can cause tissue damage. Inferior refers to the lower region of the heart. So what the ECG said was that your sisters heart was not getting enough oxygen. This sets off a red alarm for anyone reading the ECG. I don't know the exact cause of your sisters ischemia as there are many different causes, but I suggest she stay under the care of cardiologist as this is a serious matter.