It was in aCoS when Nicola approaches her for the blackmail incident. She asks Egwene to be given the same chance Egwene was, and Egwene counters with the arguments about forcing and how dangerous it was, and recalls Siuan apologizing for doing it to her.

In my opinion, that referred to her teaching session on the boat ride from Shienar, which is the only thing that matches the descriptions in context, but it could also be an indirect result of the situations into which she was flung and supposedly forced to learn faster, in other words, forced to force herself.

But that last doesn't really apply to Egwene. She was in the least danger, under the least serious stress, and had the least school-of-hard-knocks training of the Wondergirls, since most of their time spent chasing Black sisters, and fighting/evading Modhedian, she spent in the Wise Ones' tents with only the occasional Shadowspawn raid, or minor involvement in a significant event, none of which really seems like the sort of thing that would stretch one to the limits of her capabilities.