To pump or not to pump

I have to go back to work in about 2 weeks and I'm freaking out. My mom's going to watch Alessia, so at least I don't really have to worry about daycare. I just don't know what I'm going to do about feeding her. I've been exclusively breastfeeding her this whole time - she's only had maybe 5 bottles of formula her whole life (we had some difficulty in the beginning), and am having a hard time figuring out if I want to give it up. I find this so ironic because even when I was pregnant with her, I never thought I would breastfeed. Then when I did decide to do it, I figured I would do it until the end of the summer and supplement with formula. Now I just don't want to give her formula at all. I have no problem with formula or other moms using it. For some reason I'm just having an adverse reaction to having to use it myself. My plan was to pump in the morning before going to work and sending her with at least that milk at my mom's and then nurse her in the evenings. But now I'm thinking I want to pump during the day so she doesn't have any formula at all.
I teach middle school, and if there are any teachers out there you know how difficult it is to find spare time and privacy. And to add to it, I was given an overload this year because they couldn't find another teacher. So I'm looking at my schedule and realize that I could have time to pump once in the middle of the day, but I have to ask my principal to schedule that period as my prep instead of a hall duty. No big deal, right? Except that I'm a big chicken. I have crazy phone anxiety and can't even bring myself to call her. Instead, I just sit here and worry she'll say no when I do finally ask, and then what do I do? I brought this up at my moms group this morning at Postpartum Place, and they were just like "don't ask, demand it!" They're much braver than I am! Well, it's too late to call her today, so I guess I'll have to try tomorrow. Wish me luck!