FYI: I have no control over how this question is used. If you're presented with nothing but "____ geltī eman" and no translation, then, yes, both ñuhe and ñuhī should be correct. However, I simply cannot say that Ñuhī geltī eman is an appropriate translation for "I have my helmet", because it isn't. It's incorrect. I can't allow that translation to be accurate, but I can't seem to prevent the sentence listed above from appearing. This is a problem on Duolingo's side, so the complaint should be escalated to their forum.
This is not always true. It depends on the declension. Ñuha is quite distinct most of the time. Here is a link how all the adjectives decline: