It isn't monosyllabic 'en-da'. If you add a 'ku' when it isnt a monosyllabic verb then the 'ku' becomes a subject infix
Well, it's not monosyllabic, the stem is |e|nda| ("nd" is, in this case, a single consonant), but yeah, it's one of the exceptions, and it does act like a monosyllabic verb in keeping the kw in some situations.
But ... both forms are correct and both should be accepted:
ninaenda = ninakwenda