That sounds like a difficult corner to write yourself out of, but you can write around it. I have a non-zero amount of characters in my Dragonfeathers universe who are ancient, immortal beings - they've been around for hundreds of thousands of years, and are obviously extremely competent. Writing for them is hard, but I simply need to write in different challenges for them than I would a mortal character.
For instance, if I can't challenge them with a life-or-death scenario, I can have them struggle to keep the mortals around them alive. If I can't challenge them intellectually, I can challenge them emotionally and ethically, by giving them heartbreaking and difficult decisions to make. And if I can't challenge their courage, I can challenge their emotional resilience.
For your lie-detector character, perhaps instead of challenging her with decisions such as "Can I trust this person?", you could challenge her courage, her resourcefulness, and her ethics instead.