When she is thinking she can take down 5 AS if she acted fast she didn't know about the forkroot, they start talking about forkroot and she immediately starts thinking about what Nynaeve had told her about the stuff.

Once she meets up with Silviana she is thinking she's at a point where she can embrace the source, but with no idea how much weaker she may be, all she knows is the story she heard from Nynaeve which would include the difficulty in channeling. There is no reason to call it out again here as we the readers already know all of this! It's shown over and over in the books that even a very weak dose of Forkroot dampens her ability dramatically... she couldn't have broken a shield held by Sorilea!

Knowing Silviana is "far from weak" and that her own power would be lower by some as yet unknown degree and given no opening to even attempt to grasp the source she realizes she is stuck.

I agree that Amys is likely not as adept at shielding as an AS which likely contributed to Egwene's ability to break the shield, but Egwene was also certainly at a lower strength level in that scene too.