a lot of people can keep up some supply with relatively few feedings. once breastfeeding is "established"- your body can keep 'just enough" in there until all the feedings stop.
If I were you i would slowly cut down... but keep up the "regular" skin-to-skin feedings- those are what maintain supply. Formula is ok... but too much might leave her over-full if it is spaced close to when you will have her feeding/s. I found the easiest feedings to keep long-term were the morning and night feedings.
Regardless of how long you keep going... any breastfeeding is awesome. There are plenty of reasons to keep breastfeeding for a while still- if you are "on the fence" about whether to keep going... that said, there is nothing wrong or bad if you decide to quit!
I am just saying that it is NOT an all or nothing thing to do... you can have varying degrees of breastfeeding all the way from exclusively breastfeeding, down to just one feeding a day. for some benefits of "extended" check out this site:
http://www.kellymom.com/bf/bfextended/ebf-benefits.html
the benefits actually peak from what I have read at about 1 year old, and then slowly decline over time. I can attest that my daughter NEVER got sick until she weaned- not that I feel guilty about it. but- the pros might be worth it if you are willing to keep a feeding or two just a little longer (whether that means 2 weeks, a month, or a year) No one can make that decision for you!
BTW- if you are curious, i breastfed my daughter, at least one feeding per day up until she was 21 months. Extended breastfeeding isn't for everyone. Do what you feel is best for you, her and your family!