honestly kay, i don't know if you've been reading my "introducing two cats, help" thread, but this sounds like layla.
if this were a dog, i'd say something was wrong physically or behaviorally. but with a cat? she could just be a b*tch. for instance, there is nothing physically wrong with layla either, but she is a horror.
the running up and down the halls thing - that's common with cats. charlie does that and is playing. but he'll let you pick him up.
with layla - when we try to pick her up, she starts hissing at us when we get close. then if we pick her up anyways, she groans and moans deep in her chest. and when we put her down she swipes at us or bites us really hard.
now, for layla - when we brought her home at 8 weeks she was very feisty and would hide and then pounce on you and attach herself to your legs to attack, etc. so she's always had a mean streak.
if maggie is normally NOT like this and this is a sudden change in behavior, then ask yourself:
have there been any changes in the house?
any new people? animals?
did a spat occur with another person/animal that you thought was resolved?
if it's none of the above, then i'd ck with the vet. she could have something that makes her tummy hurt and that's why she doesn't want to be picked up. or she may have something else that is just putting her in a general bad mood.
just remember - often times, cats can just be mean and there is no explaination for it at all.
i wish you all the luck with her!