well here are my thoughts...first, the way she was with the girls day, i really feel strongly this is an attention thing. this may be just me, but i would play with her. it sounds like maybe after a long day at school she just wants some time with mom. my son gets really whiny and bored in the evenings, and sometimes i just have to STOP what i'm doing, whether it's making dinner, doing chores, or playing on the computer trying to relax, and get down on the floor with him. all he wants is some time from me. it sounds like to me that she's just wanting some attention, and probably acting out as a way to get it, we all know kids act out to get attention even if it's negative attention. think about it - when she throws a fit about her socks, you stop what you're doing, talk to her, try to reason with her, help her clean her toes, etc. that's the attention she's wanting.
my S. thought about the socks is, put your foot down (no pun intended!) my son does this sometimes too, just refusing "that" pair for whatever reason, then he'll pick another pair and those aren't good enough either...BS! socks are socks (he usually does it with his underwear) put them on and that's the end of it. i would recommend timeouts to curb this - with the way she is about attention i bet it will nip it in the bud if she spends a few minutes alone with no interaction or attention. she'll probably be ready to put her socks on after that.
as far as not wanting her to be disappointed, i would start working on that...kids need to learn how to deal with disappointment. it's part of life. tell her what the plans are, if you're excited about something fun, share it with her. if you're worried something might happen, let her know, "i hope it doesn't rain" (or whatever), "i'd be sad if we couldn't go...but we'd find something else fun to do wouldn't we?" keep it positive. don't keep her in the dark, "afraid" because something might happen...let life happen and enjoy whatever comes. kids do get disappointed, but if you think back, maybe your distress over her disappointment might have made the situation worse. instead of trying to "protect" her from disappointment, teach her how to deal with it and go on. she'll benefit from that lesson later! remember our #1 job as moms is to be teachers. it's our job to teach them how to get along in this world.
just my two cents...oh (sorry, i ramble!) and as far as playing with her, don't forget to involve your son as well...teach them how to play together, games they can both play, etc. i'm not saying put everything on hold every night to do nothing but play with the kids, but you'd be surprised how big a difference it can make, even just 30 minutes of undivided attention.