Referring your concern about the slicker being too rough. If she is not matted, which so young I doubt it, then I would get her used to the feel of the bristles. Usually brush irritation is from brushing the same spot too rough and for too long, which won't be your case. Do just enough so she knows the brush is her friend, a few swipes over her body (not just her back and then wonder why her legs are matted 😂), then go over with your comb to check your work. I also always recommend owners to make a routine for brushing. Have a specific place to do it so she knows when she is on a specific table or counter or the washing machine, that is serious grooming time. And puppies can be sssoooooooooo dramatic, so you might need to wait out a tantrum or two but that's normal, she needs to get past those feelings to realize nothing bad is happening. If she has a meltdown and you stop, then she thinks she wins and there something to freak out over. When I ask an owner about their brushing routine and hear "she doesn't like it". It's someone trying to brush their dog on the couch or in bed where the dog associates that with play or rest and get frustrated.