When you are away from her you may be very surprised at how much you need to express for your own comfort, and also at how much you get out.
I wouldn't worry about the formula - just give her whatever EBM you have and food and water.

I went back to work full time when my DS was 10 months old. I would express at lynch and maybe one other time, depending on how uncomfy I was. He decided he didn't really like EBM, so he had some on his cereal and had food and water during the day. He then would have a feeding frenzy when I got home, and unfortunately started waking up for more night feeds.
The main problem (other than lack of sleep) I had was Mondays - when after a weekend of feeding I had a huge supply.

If you go without DD for a week you will have to express for your own comfort - I'm guessing 4 times a day. So you may want to get a double pump and get good at double pumping!

Before you go back to work, have a practise day or 2, where you leave DD with someone you trust and go play for the day, taking your pump! Then you'll have a better idea of what's involved.