I had dd2 last summer when dd1 was 4 and my dd had also had alot of attention up to that point as dp and I are both at home a lot of the time so she was just used to having us around for her.
I told my dd1, and still do, that she will always be my first baby and she will always be special because of that.
Something that I realised after having dd2 was that dd1 had been worried when I went into hospital b/c she thought the baby would hurt me, so some reassurances for your dd on that score may help.
It may also be an idea to ask dd if there is anything that she has been thinking/worrying about to do with the baby so that you can address any concerns she might have but hasn't mentioned up to now. It was always my worry that it is hard to know what's going on in their minds at a time like this and how much it is affecting them, but that they won't always volunteer that.
I am sure that your family will be thinking of the effect on your dd also and will no doubt bring gifts for her aswell as for the baby, and also lavish attention on her still so she doesn't feel left out. Everyone that brought us baby gifts gave something to dd1 too - people are very considerate. And of course a gift to her from the baby when she first sees him/her will help.
In the first few days I think my dd1 was surprised at how little dd2 did and got bored with the lack of interaction, so let your dd know that the baby won't do much but feed and sleep, but that she can be a great big sister for the baby by helping you to get changing things etc. (We made quite a thing about dd becoming a big sister cos she was so excited about that)
Sorry it's a bit waffly but just typing things as I think of them, it's too late to think any straighter than that!
Good luck on Mon, Sure you'll do great