Translation of "Tenaz" in English

Ella es muy tenaz por más que no lo luzca.

She is persistent though she doesn't look so.

Me he pasado las tres últimas semanas peleándome con un resfriado tenaz.

I have been battling a stubborn cold for the last three weeks.

Eventualmente se rindió de hambre, pero su tenaz defensa le dio a Napoleón suficiente

He was eventually starved into surrender, but his stubborn defence bought Napoleon enough

Es un niño muy competitivo y tenaz, que se enfada si no se esfuerza al máximo.

He's a very competitive and determined kid who gets upset if his best isn't the best.