Silviana is covering all of her bases ... she certainly doesn't want to run the risk of Egwene waking up in the middle of the night, breaking a too weak shield and vanishing via gateway ... thus the "this child is tricky" comment. Let's face it any Sister could hold a shield on a sleeping woman.

Katerine was just bitching that she's stuck with the task. It's in her nature to hate being forced to do tasks like this! Note how Silviana treats Katerine in this moment ... like a petulant child! Her response is "Because I said so" something you say to a bratty kid!

And Egwene still had so much Forkroot in her she was only barely able to Channel at all... not to mention she was exhausted from being captured!

KOD
Prologe

Apparently she did not. Katerine flushed, but she said no more. The glow of saidar surrounded Silviana, and she took over the shield smoothly, without giving any opening when Egwene might have embraced the Power herself. She was certain that she could, now. Except that Silviana was far from weak; there was no hope she could break the woman’s shield. The gag of Air disappeared at the same time, and she contented herself with digging a handkerchief from her belt pouch and calmly wiping her chin.

First note that Egwene is only now able to even embrace the source and we know from history that Forkroot dampens your strength for hours (as we see all through the rest of the book Egwene can channel only a trickle). This quote gives absolutely no indication that Barasine alone is capable of holding a shield on Egwene for long!

Then let's take this into consideration:

TGS
News in TAR

The two glanced at her with annoyance. "The shield," Barasine said. "We've been instructed to always have at least two to maintain it."

"Oh, for the. . . ." Egwene took a deep breath. "If I vow not to embrace the Power until I am properly back in the custody of another Red sister, will that be enough for you?"

The two regarded her with suspicion.

"I suspected as much," Egwene said. She turned to a group of novices who were standing in a side corridor, pretending to scrub the tiles on the side wall while they gawked at Egwene.

"You," Egwene said, pointing to one of them. "Marsial, isn't it?"

"Yes, Mother," the girl squeaked.

"Go and fetch us some forkroot tea. Katerine should have some at the study of the Mistress of Novices. It's not far. Tell her that Barasine requested it for use on me; bring it to my quarters."

The novice scrambled off to do as asked.

"I'll dose myself with that, and then at least one of you can go," Egwene said. "Your Ajah is collapsing. They're going to need all of the clear minds they can get; maybe you can convince your sisters that it is unwise to let Elaida execute Silviana."

The two Reds glanced at each other uncertainly. Then the spindly one whose name Egwene didn't know cursed softly and hurried away with a flurry of rustling skirts. Barasine called after her, but the woman didn't return.

Barasine glanced at Egwene, muttered something under her breath, but remained in place. "We're waiting for that forkroot," she said, staring Egwene in the eyes. "Keep moving on to your quarters."

Always instructed to have at least 2 maintaining the shield (implying that if weaker Sisters were holding it there may be need for more), Barasine muttering under her breath and calling for the other Red to return ... and there is no evidence that the other one even left the link ... no reason to assume Barasine wasn't in control of a link and the other woman's strength was still there.