Nina doesn't have much practice... Being. She talks in almost exactly the same way Nick does, and Nick and Nina both keep getting distracted by each others' conversations.

The machine that makes medical nanos is one of the things that are nontrivial to maintain. If someone spent a month or so learning to use Nick's tools and bought lots of spare parts, it would last for a century or two, but without access to facilities that are not on Nick's ship it will not last forever. The nanos themselves keep indefinitely, though, and one dose covers one mortal for a whole month. He has entire crates full of them, they'll last for quite a while if she buys all of them.