aloof kitten

I have six foster kittens(10 weeks old). They are all so different in personalties and all of them are great with people except for one. Samatha is not afraid, she dosen't run and hide or try to bite you when you pick her up she just dosen't seem to like human attention as much as the others. Twice in the last week she has sat in my lap for a couple of minutes to be petted and will purr but then jumps down and goes away to play or sleep. She will not jump in your lap, you have to pick her up. If you reach down to pet her when she comes close she will usually move out of your reach. She does love to play with you with a toy and will allow you to pet her while she is playing. She will stay close to you as long as you are not petting her and will hiss sometimes when I am giving her meds but never does more than hiss. I could understand it if I thought she was scared but I don't think she is. She loves the dogs and plays with them when they are together but just so aloof with people. Will she get over this with time or do you guys think she will always be abit aloof? I spend a lot of time playing with her and trying to show her that being petted is a good thing. I try not to force anything with her except for her meds. She was like this before we started her treatment for her URI. She didn't hiss at me today when I gave her her meds so she must be getting use to that. Any ideals would be great. I usually foster dogs so am new to kittens. If this was a puppy I would know what to do, but am stlll learning with the kittens. Help please!