I'm sorry I'm not a psychologist but I am a parent of a 5 year old. This is normal. 5 is the age when they start exploring and learning about bodies. She just wants to be like mommy. So of course she will prance around wearing a stuffed bra. Its fun.  There is nothing wrong with pretend so long as the child is not endangering herself or breaking the belongings she's playing with. There is however something wrong with a father that wants to use that in court. Seems like hes just grasping and has no hard evidence of bad parenting.  I hope all turns out well with the custody hearing.  Not that I know any serious details of either sides parenting type but I hope that the child will be placed with the parent that will be open minded to a 5 year-olds way of learning.

My little girl is 13 soon, and wearing bra's all the time, obviously!

But I remember when she was 5 or 6 she was interested in wearing my bras and stuffing them with (like your grand daughter) anything she can find to do it with!
About this time she would also want to shave her legs whenever I was shaving mine. After about 2months I decided to buy Kate her own training bra, and blade free razor, so she could feel all grown up but still not be harming herself (cuts from shaving, cup bra problems)

She eventually (around 7) grew out of that stage, and didn't really become Interested in it until she got her first period.

Now the issue of the father... I can see why he doesn't think it is normal, I remember my dad when I was growing up. I reached puberty quite early, and he (like I'd say her father is now) is feeling quite uneasy about his baby growing up.

Anyway, let me know how you go, and good luck!!

Five-year olds do not normally become obsessed with what goes in a bra unless that five-year old is exposed to seeing what goes in that bra. When mommy keeps herself covered and the daughter is involved in normal five-year old activities, this doesn't much occur to that age. The other exception is when 5-y.o. watch mommy breast-feed younger sibling. A natural curiosity is piqued. Does mommy have cable TV? What is she watching? What type of magazines are laying around? Remove these two elements, replace them with good children's books, healthy interactive playtime between parents and child, and this obsession will dissipate.

Sweet heart  , Your grand daughter is just growing into a young woman it is indeed completley normal as a 3rd grade teacher Some kids expose there undergarmets etc. Its just them saying hey im a big kid now. My own daughters just started wearing traning bras its completely normal for kids to be kids :-P ooh and good luck in court