I was pleased to find this post, as I wanted to find her grave after having read her book Tide Race while I was on Bardsey. I found Sir Henry easily enough, but the grave three in was for the Coates family, with Becks and Edwards on either side. I couldn't see a Chamberlain anywhere.
I went back today after double checking the names and found it. Her grave is also along side the path, just two plots to the left from Sir Henry Lewis. Her inscription is on the very bottom of the base of the cross, and it is around the back, so you wouldn't see it if you just walk along the graves looking at the front (as I did!)
Here's a picture of the grave. Her family grave is under the cross on the left, and Sir Henry's is the low profile one at the right. It's in a sad state, with the top slab all broken up.
Here's her inscription:
Warren