I would suggest just telling your daughter that it's a natural (and healthiest) way for babies to get their nutrition. Our society has way too much of a hangup about women's breasts. I can also guarantee you that when you're around others, they'll be far less offended by a breastfeeding baby than they will be about a screaming baby (particularly on an airplane). Also, I highly recommend you find a local La Leche League group for support - for yourself and your daughter - she'll be able to meet the siblings of other breastfeeding mothers and the normalcy of the process will be re-enforced.
My son was much younger when I breastfed his baby brother, but I remember him taking his baby doll and "nursing" it - lifting up his shirt and all. (And, yes, I'm one of THOSE mothers that believes in promoting the nuturing side of boys as well, so he did have a doll). My boys are now 10 and 13 and breastfeeding is the only decision I've made that there's no doubt in my mind at all that I did the right thing. They were extremely healthy as babies/toddlers, even being in daycare. We later learned that they have a genetic auto-immune disorder (celiac disease) and are allergic to dairy, so I know that my breastfeeding really helped keep them as healthy as possible in those early years.
Most importantly, you'll be setting such a fine example of nurturing for your daughter.