From the commentary it seems like this woman knowing kept herself from reaching her full potential, but I'm making an assumption on that...

If that assumption holds true we can start some logical eliminations

1. Likely not a member of the Black Ajah ... these are women actively seek more power and wouldn't purposefully limit themselves in this way. Verin being the obvious exception here

2. Not likely a Blue either ... Blues are typically political animals who seek higher rank within the Tower so this seems like a poor choice

3. Doesn't seem likely that this would be a mechanism to hide their true strength since women can sense both current and potential strength in others

4. Not likely one of the strongest Aes Sedai as they all jockey for position too much

So that leaves us with middling sisters with little or no political ambition within the Tower ... Perhaps one of the women in Cadsuanes entourage as they seem unconcerned with strength and more focussed on skill.

Perhaps Samitsu is our gal since her Talent with Healing is so strong she probably rarely needs to draw her capacity in the OP? I don't think her age is ever stated In the series though, but most of the women with Cadsuane seem to be experienced.

Alternatively, because Samitsu may not fit the age outlined ... It could have been Merilille ... She seemd more focussed on being an Ambassador and wouldn't have achieved a ton within the Tower regardless of reaching her potential.