Finding the perfect gift for someone who loves to knit can be a challenge. But once you understand what your friend likes, you can narrow down the options and find the perfect knit gift for them much easier. Personally, I would choose something that was removable (more like a safety pin and not just a closed loop). Gifts of luxury yarn such as cashmere, silk, mohair, baby alpaca or fine merino are always appreciated by knitters.
But if you want to give something special, consider a skein of Simply Socks Yarn. This yarn is dyed to make a pattern mostly just stripes when woven, so it's a “fun surprise” when you see the final design. And if you buy all your yarn online and don't want to go to a store to have it rolled up, like Leimkuhler, it's good to have it on hand because having your yarn pre-rolled sometimes costs more, but you can't really weave without it being rolled into a ball shape. If you are looking for unusual gifts for weavers, then weaving inspired jewelry (such as these earrings or this necklace) could be a great idea.
Although yarn seems like an obvious gift for a knitter, it's a difficult gift to buy without a specific project in mind. If you don't know much about knitting, you may end up with something that's difficult to work with. A row counter is also an excellent choice for knitters. It only goes up to 99, but that's more than enough, unless you're making a blanket that doesn't normally require much row counting anyway, unlike a sweater.
And with what seems like hundreds of options online, your weaver is guaranteed to find something she likes.