It's probably just a comfort / security response. Anything warm and furry will remind her of snuggling up to mum as a newborn, and as animals go to sleep, something that helps them feel secure will always settle them off.
I have got exactly the same problem with my kitten. the thing with him is that he sucks on any part of me he can get too. Last night he sucked on my neck and today i have all these little bruise type markings on my neck which look as if I have had a mad passionate night of lust. ha ha chance would be a fine thing.
seriously the vet told me he does it because he was taken away from his mum too soon,
A lot of 'oriental' type cats do this....as she gets older she will probably seek out your wooly jumpers. It is perfectly normal....and just one of the many crazy things we love about our cats.
my two boys do this and they are now a year old, but at bedtime they cuddle up together and suck on the furry blanket, kneading and purring, it is just so sweet.