Fetching path is not possible, please see the FAQ: Native Gallery for Android & iOS [Open Source] . You need to keep a separate copy of the image in e.g. temporaryCachePath and share it instead. If you are using SaveImageToGallery with an existingMediaPath, then you can simply share the file at existingMediaPath since NativeGallery simply copies the file to Gallery, not moves it.
EDIT: Corrected FAQ link.