Sempai just means "Senior" a student that is higher ranked or has been there longer is just that... A senior student. It has no connotation of a relationship other than they are also learning, but have been around the block more than you. Why would you be squemish about using the Japanese term when you practice a Japanese marital art. Do you not use terms like Ireminage, shihonage, and jujinage in favor of terms like entering throw, four corner throw, and figure ten throw?
Secondly, how do you know what kind of relationship she has with her seniors? Just because she isn't Japanese doesn't mean she cannot relate. If that were true that one cannot understand a sempai relationship, can you honestly say that an American can understand a Sensei relationship... can one pass on any knowledge of Aikido without at least some knowledge of this relationship?
Unfortunately for you Ryan, Ron is right. Sempai/kohai relationship is impossible outside of Japan.
And as Ron is your sempai on Aikiweb now you have to bow very deeply and agree with everything he said.