As you know Nadia is older than Damon which means she is stronger but in the recent episode where she was looking for Katherine's tomb she took damon by his throath but Damon was some how stronger and removed her? How can this be when she is older.
No show is perfect, so I see it as nothing more than a little shark jump.
The only logical answer I can congure up is that Nadia knew that aggression and violence against Damon wasn't going to help in finding the body. Plus, Stefan was in the room. I'm sure Nadia can take them both but why waste time? Also, Mia was a traveller, and they are always on the move, so Nadia probably had a tight schedual, as did Mia.
I'm sure that if it were just Damon and Nadia in the room and he did something to really set her off, Nadia would win in a heart beat.
Blood consumption also has a factor. Stefan drank animal blood rather than human for over 50 years, while Damon lived off human blood for his whole life, which is why Stefan got his ass handed to him in the first 2 seasons. Imagine if Stefan a solid human blood diet, along with his Ripper hunger, he would drink endless amounts of blood, deaming that age strenth fsctor useless if he were to fight Damon.
To your question, Damon has had a solid human blood diet, we don't know a lot about Nadia, how she became a vampire, learned about Katherine, what kind of diet? so this is probably why Damon could shrug her off.
Krobat could be right.
Its all speculation until we learn more about Nadia, whos origins are supposed to be revealed in a few episodes, so we'll find out then.