- SPOILERS AHEAD TO STARGATE ATLANTIS!
- No, they were not.
- They were healing/reviving her; we just don't know how.
- We don't know if the Nox know how to ascend.
- The Alterans had to research how to do it.
So, the Nox were not trying to ascend in that situation. They were actually trying to help Lya. She was hurt after being attacked by the Goauld and they were helping her. We don't know much about the Nox culture/technology, but (just as the snakes have the ability to) they have the ability to bring someone back from the dead if they need to.
Despite this amazing ability however, the Goauld do not have the ability to ascend. And from what we know there is nothing to say that the Nox have the ability either; despite how advanced they are. From what we see we know the Nox have the ability to make things invisible, make cities hover, bring beings back from the dead, turn the gate on without dialing, and somehow know if people are only pretending to sleep (might not be so impressive, but...).
Mind you, we have no clue how these things work for them, but we know that they can do each of those things and likely more. Also keep in mind, that in SG1 Season 2 Episode 21 "1969" Cassandra had that device on her hand that allowed her to dial the gate with a swipe of her hand. Even if this was a 'pre-programmed' dial there is nothing to say that Lya didn't have that (even something embedded into her skin or whatever) to allow her to do that as well.
Now those are all impressive abilities, but we never see or hear of the Nox ascending. The Alterans are the only ones (minus Anubis, Daniel, and the Ori) that have attained ascension. Technically, the Ori were still Alterans when they learned how and we know that Anubis and Daniel only ascended because of the knowledge they got from the Ancients.
However, the Alterans learned how to ascend through research:
From Stargate Atlansis Season 1 Episode 3 "Hide and Seek" we know that the Alterans somehow found out about living beings of energy and managed to lure and trap one in a containment device. This being they studied and actually researched how to ascend.
Assuming that the Nox never discovered or cared about these beings there is no guarantee that they would have ever learned how to ascend. If the beings of energy only existed in the Pegasus galaxy then the Nox never would have even gotten the chance...
In the end, the Nox are extremely advanced... We just have no real hint as to how advanced. All we know is that they are one of the other three super races that were allied with the Alterans. They seem to live a peaceful life and from what we can tell they don't even seem to leave their planet unless it is absolutely necessary...