4.5 Yo Hiding Food

I don't think I would make too big a deal out of it. Maybe she didn't really take the food to her room because she was hungry...maybe she just did it on a whim and when you questioned her about it, the logical thing for her to tell you was that she was hungry.
My stepson used to hide food...but not because he wanted to eat it later...much the opposite...if he didn't like something that he was supposed to eat for lunch or dinner he would secrete it in pockets, etc...then go hide it in his bedroom...lol.
The cookies that she took...that the two of you had made together might have just been really important to her...since the two of you had worked on them together!!
Personally I wouldnt make too big a deal out of this....it is probably just a passing phase

Do you forbid her to have a snack after a certain time? My 5 YO daughter is often hungry at bedtime. They are growing, yet have little tummy's. I usually give her a cracker or plain popcorn and that is enough to hold her over until breakfast.

Just a thought based on my own experience. I remember being around 6 when I start hiding food that I didn't like under the cushions of the seat and I would take it later to the garbage when nobody saw me.
My mother never notice until one day I forgot and she was cleaning and found my secret place. Well, that didn't end up well and I never hide food again...well that is not true, I remember trying to hide it on my cheecks and go to the bath which didn't work that well either, oh and then spit in my napkin, lol
No, I was bulimic or nothing like that,I just didn't like some food and in my house was not chance to say I don't like this give something else.What ever my mom cooked is what we et and period.
Now, I am not saying that your daughter is throwing food, or that you should give her a menu, maybe she really is hungry, but just wanted to give you mi own version on why I did hide food from my mom.

Maybe, your going back to work is significant. At home everything is hers and she has noone to tussle with. Everything revolves around her. Now she is competing with a bunch of kids for everything. Toys, time with teacher, the swings, you name it. Maybe, and I'm no child psychologist by any means, maybe she is holding onto the food because she is feeling like she has no ownership or control of anything at day care. Food is the one thing that is your own at daycare (well, backpack and food) They put you in a little chair and give you your little portion. No tussle. So, perhaps she is getting a sense of control from food. Or she is in a mind set of having to stake her claim to things, including food. And that's why she is hoarding the food at home. Maybe I'm just talking off the top of my head and have no idea what the hell I'm talking about! Just a theory.