ok,i'll see if i can be any help.
First of all, how much do you hold her and how often are you around her? Does she unball and let you pet her after you pick her up? Does anyone other than you ever hold her?
i don't think its anything with her nervous system, and i don't think another hedgehog would help.
My hedge Mr.Prickles,(who we have had for almost a year) still acts the same as your hedgie but Lady Velvet is very friendly and is ok with being held. we try to hold them like every day so they get used to it but Mr.Prickles still does not like it.
I think different hedgehogs just like people more than others, we have had 2 or 3 litters of babies and all of them have been different,some of them really like people and some just don't.
Maybe just try to hold her as much as you can and just keep her around people whenever you can and she might get better about being more friendly.she might just be really shy like my Mr.Prickles so its VERY NORMAL.
hope i helped but i'm sorry if i did'nt.