Read her interaction with Tattletale in the epilogue again; she is not well spoken, but she is both moral and clever enough to understand that taking down Teacher is possible. People who are supposedly "intelligent" but are actually just book-smart or a very specific kind of intelligent (eg; with a narrow focus) tend to miss things other people have an intuitive grasp at.

This is why some so-called "thugs", which have little formal education can become leaders and even very successful financially (and not just as criminals, but also as politicians, musicians, community representatives, and so on). Raw intelligence does not equate to eloquence or even what most people stereotype as intelligence; a thousand years ago the average cognitive abilities of the average person were the same as they were today, so most measurements people use are obviously false.

Rachel didn't trust Taylor at the start (and rightly so, Taylor wanted to betray them), but instead of expressing it eloquently, she expressed it by attacking. At the bank, she's the first to suggest busting out the front (with a complete lack of eloquence stating they can go through the wards). She mouths off to Hookwolf when she knows she can get away with it, but despite the Siberian doing things that would piss Rachel off, no immediate fight ensues, and Rachel as far as she's concerned remains polite - so she isn't just an "attack dog", she does calculate risks. The list of choices she makes is rather long, and overall, they are better choices than most others make.

If you read up on what she suggests and what she actually does while ignoring the phrasing, you see that in fact she's not stupid. Plenty of characters are stupid. Rachel isn't. She really was screwed over by her power, and before that by society. Even so, when all she wanted was to carve out something as her own, she managed to become something more once people gave her support over time.

That being said, she isn't in my top five favorite characters, but is still one I think fondly of.