Well I bet you were glad to hear from her!
There is no doubt that she would appreciate being able to confide in you at any time, especially a difficult time for her such as this.
Your decision not to talk about the relationship between you is a good one.
As much as I'm sure you are longing to know what she is feeling and when the "break" will end, it is most possibly something she is not even thinking about, and is unaware of the painful effects this is having on you.
However, her calling you to talk is a good sign that she is still thinking about you a lot. Her deciding she wants a break from the relationship was most probably for what she said, to sort her feelings out. For instance, if she was aware that she was becoming increasingly depressed to begin with, she may have used the "break" to slightly distance herself from you to determine if the depression was anything to do with the two of you. On the other hand, it is also possible she didn't want you to see her in the depressed state, because she didnt want you to think you were the cause of her depression.
She probably just doesn't want to make you unhappy by sharing her depression. i know it will seem to you like you would have been happier without the break, by trying to help her work through it, but if she is withdrawing from everyone this wouldn't have seemed like a good option to her when she made the choice.
I think the Valentines gift was a good idea, to let her know you still care for her. Remember, you have been together for two years, and I am sure her feelings for you have not just vanished, most likely just clouded by other emotions or problems. I am sure she will appreciate the gift, and be grateful that you are thinking of her.
Depression is a strange thing. When I was depressed I also found myself in denial - saying to myself and everyone around me that I was not depressed. I did not have a girlfriend at the time, which in hindsight was probably a good thing. I feel that I might have done the same thing as she did, in order not to depress my partner further, had I been with someone at the time.
I started noticing that everyone said I seemed depressed and withdrawn.
I dismissed their comments, and continued about my life. However, I ended up noticing myself I did not see family and friends hardly at all. I started thinking about the depression consciously from this point on. Every day I made extra effort to be nice to people, and chat and smile. It took a fair while, but I feel things are back to normal.
When she says the space she needs is day to day, I can relate to that. My mood towards contacting people changed greatly from hour to hour when I was depressed.
I am sure she will overcome the depression and things will return to a happy state between you.
Good luck!