Cody is the same way, and for him, it doesn't matter what the leash or harness is made of. In four months, he has chewed 1 collar, 4 leashes, and more than 6 harnesses, all of varying materials. Most of that was in the first two months. Luckily since July I have only had to replace the harness twice and the leash once.
Does she chew the collar or leash while she's wearing them or does she find them and chew them?
What I have recently done is find a collar that fits well and that he can't reach to chew while he is wearing it. The only time I take that off is when he is getting a bath. The harness comes off as soon as we come home from a walk/ride and it goes on top of the refridgerator, as does the leash. This is because if he can reach it, he will chew it into hundreds of tiny pieces in 2.6 seconds, whether he's wearing it or he finds it laying around. I also keep an eye on him while we are are out because he has chewed through a leash while we were sitting at a table and I was having coffee with a friend.
Good luck, and hopefully someone can recommend something. While changing my habits worked for us, I'd be interested in any basenji-proof leash and collar suggestions as well