I think it depends on a lot of factors - the age of the baby, how many times a day you are feeding, the quality of your milk production, and the ease of your experience thus far, etc. Is she slepping through the night? IF not, she will, so how many feedings would you be doing at night?
With my first child, I nursed exclusinvely for three months (supplementing only at the very beginning because of low production in the first couple weeks). After I went back to work, I pumped (a pain in the neck, I know) but I was not good about pumping and pumping is never as good, so by the time my daughter was about 6-7 months, I nursed about 4 times per day and gave formula bottles the rest or for day care. I nursed like that until about 13 months. But she slept through the night early, so I wasn't really feeding at night.
With the second baby, I breastfed and pumped almost entirely for 15 months, with convenience formula bottles a couple times per week. Now that she is 15 months, I only nurse 2 times a day and plan to drop to once soon.
So, yes you can nurse part-time. I found it is better/healthier/easier/cheaper to nurse mostly and supplement. I know pumping is a pain in the neck. But if you are lucky enough to produce milk, I would try it for as long as you can. If you do decide to go part-time, I would do it gradually because you don't want your production to suffer (you need ot let your body figure it out slowly) and you don't want to traumatize the baby. Keep in mind that if she wakes a lot at night now, she won't always so the amount she gets will decline sooneer than you expect.
I think it is great that you want her to keep getting the benefits and don't want to just stop altogether. But milk supply is a tricky thing, and once you start nursing less, you may find it difficult to match her needs if you dont' drop feedins slowly. For that reason I would nurse/pump for as long as you can. She will have less feedings with time especially when you start solids so its not like you hav eto stay up at 8 feedings forwver. On a personal note, I am nursing my last baby (probably), and I will miss it very much when I am done. And I never thought I would feel that way becaus eit was so hard at first. Good luck.