"She has the will to survive."
Translation:Hun har viljen til å overleve.
In English there's both the preposition "to" and the infinitive mark "to", but in sentences like this one you still only need one "to".
In Norwegian, we use both the preposition "til" and the infinitive mark "å". It's not possible to leave out "å" here. The infinitive mark and the infinitive verb is a package deal when following a preposition.