That's true, although Shadowheart isn't the trusting type. A warning from her doesn't feel all that impactful.
I didn't mean Shadowheart's warnings only. For example in one conversation Shadowheart asks Lae'zel how other gith supposed to react on outsiders (us) coming with her. And Lae'zel answers that her people will understand her need for slaves. That's not something proving her good intentions. And she is being like that all the time.
I thought she was joking! And if she wasn't, I'd be OK with pretending to be her slave for the sake of survival.
The way I see it, arguments between her and Shadowheart are the result of distrust and prejudice between two people with equally valid points of view. On one hand, a strange creature with strange, if disturbing, customs, on the other a shady, guarded person who won't tell you her real name. Between the two, I feel the game is implictly telling me to trust Lae'zel by making her the first face I see when playing.
For contrast, when Raphael shows up the game makes it clear he's bad news. Every companion has something to say about him, and all of them say he's dangerous.
All the same, you're right. There was a lot of effort put into pointing out Lae'zel's plan is not the best idea. Plus, to find the patrol, you need to talk to Zorru and several people in the grove will block your path to tell you about Nettie. So you've reason to doubt Lae'zel and there are alternatives to her plan.
The designers clearly put thought into this, but I wish it was more blunt. It takes at lot to make me look a gift-yanki in the mouth (lolololol).