I wouldn't say ignore the hissing, because you do want to respect signs from a cat that they want you to back off, but I would say don't let it make you leave the room, or, if she's hissing because you're taking her water bowl to refill it or her litter pan to clean it, don't stop doing those things. I usually talk back to our more feral kittens at the shelter: "Uh huh. Tell me more!" and then just keep doing whatever it is I need to do. We often sit with frightened or less socialized cats, talking to them, offering treats, offering toys, but mostly just keeping them company for a while, letting them get used to us. Any attempt on their part to engage with us is met with elaborate praise and offers of treats, similar to when one is toilet training a small human. It really just takes time.
Kittens also will use their claws without thinking about it -- adult cats only use them when they need to. So she may put her claws out for balance when climbing on you, or if she gets startled, and that's not because she's trying to hurt you or she necessarily wants you to go away. She also might start chewing on you in an attempt to play or out of curiosity. I had a 2 month old kitten gnawing on my hand the entire time I was changing out the paper in her cage yesterday. She thought this was the best game ever. I was not quite as amused.
Speaking of shelter cats, if you could spare a few prayers for my shelter's little cat Charlie, who is not doing well despite everyone's best efforts (yesterday the vet gave him fluids and one of the volunteers hand fed him cat food, and some of the other volunteers and I wiped him clean and got him warm blankets), I'd appreciate it. He's a very good boy and he's only a year old. We're not giving up on him, but he's so fragile right now.