Was Aurra Sing Post-Prime In Legacy of the Force: Tempest?

I've often seen it said that Aurra Sing is post-prime when she battled Jacen Solo in Legacy of the Force: Tempest. Where does this belief come from? This seems contradictory given that most Force-sensitives grow stronger with age, rather than weaker, and the fact that her father's species was a long-lived one*. Aurra would only be 91 years old in 40 ABY.

*Relevant quote from Legacy of the Force: Tempest:

"My mother was human. My father was a ghost in the night, and I doubt even my mother knew his species—but it was obviously a long-lived one." Nashtah drew her lips back in an indifferent smile. "If I ever find out who he was, perhaps I'll be able to hunt him down and kill him."

 
If it comes from the following quote*, then that isn't really an indication of her being past her prime, as of course she wouldn't be "a well-known killer of Jedi anymore" seeing as even as of A New Hope the galaxy at large believed that Jedi were a "hokey religion" with "ancient weapons", and that "The Jedi are extinct. Their fire has gone out of the universe."**

*Relevant quote from Legacy of the Force: Tempest:

"I am curious about how you chose Aurra," Leia said. "She's hardly a well-known killer of Jedi anymore."
"And even if she was, this isn't the kind of job you'd look up an eighty-year-old woman for," Han pointed out.

**Relevant quotes from A New Hope:

Han Solo: [laughs] Hokey religions and ancient weapons are no match for a good blaster at your side, kid.
Luke Skywalker: You don't believe in the Force, do you?
Han Solo: Kid, I've flown from one side of this galaxy to the other. I've seen a lot of strange stuff, but I've never seen anything to make me believe there's one all-powerful Force controlling everything. There's no mystical energy field that controls my destiny. It's all a lot of simple tricks and nonsense.

Darth Vader: Don't underestimate the Force.
Grand Moff Tarkin: The Jedi are extinct. Their fire has gone out of the universe. You, my friend, are all that's left of their religion.

The problem is that this is from the LotF era where the Jedi order is fully re-surged...... and Aurra hasn't been killing them. Moreover when looking at the novel itself Aurra doesn't come off as any better than Leia in the fights they are involved in. In fact they come off as peers more than anything else. 

Aurra is directly stated to have declined in Coruscant Nights from where she was when Aalya equaled her and there's nothing to indicate she grew again. Force users growing more powerful with age is dependent on their activity, not the age itself.

@HeartoftheForce I'd like to see that quote please, but it doesn't really prove anything since Coruscant Nights takes place in 18 BBY, and the fact she contended with 40 ABY Jacen and you believe her to be a peer of Leia directly contradicts your following statement that "there's nothing to indicate she grew again."

There's this, for whatever it's worth.