Can I respond to Elesh Norn's ability?
No, you cannot do that.

You cannot target Elesh Norn with Teysa before Elesh is on the battlefield. However, as soon as Elesh is on the battlefield, its static -2/-2 ability is in effect, and your tokens will die as a state-based effect, before anyone gets priority and the opportunity to use regular spells or abilities. Note that Elesh's ability does not resolve, because it does not go on the stack. As long as Elesh is on the battlefield, the ability is permanently active.