How comfortable with/supportive of breastfeeding has your pediatrician been until now? I think sometimes peds will see that a mother is distressed or concerned about a BF issue (for lack of a better word) and, in an effort to reassure (or take an "easier," more scientific approach), will simply open up the formula option, so that mom and doc can be "sure" that the baby is getting what she needs. It's an easy way for him to reassure you, to give you bench marks (like 32 oz/day) that you can both point to and "know" that you're doing things right. But (and this is why I ask about his attitude about BF up until now), that position is not actually helpful or scientifically/medically valid. The fact is, as you've heard I'm sure many times (and you can even hear from the formula makers themselves), formula simply isn't as good for your baby as breast milk. The 32oz recommendation is for formula and/or cow's milk (though, as I'm sure you know, you don't want to introduce cow's milk until she's at least a year old), and has nothing to do with how much breast milk your baby should be getting. Mother's milk is a different thing altogether. We don't honestly know how much is enough; different women's milk is different, different babies are different and different stages and ages are different. There are no guidelines except those that your baby gives you. If she's wetting enough diapers, pooping enough, and growing enough, then she's getting enough. Not only that, but at around this age, babies not only get more efficient (so they nurse for less time; and your daughter's feeding times are totally within the norm) but they also get far more interested in the world around them, so they become very easily distracted. Haven't you noticed how sometimes she will pop off the breast and smile at you, or look around, or want to engage with her world, but when you go to put your breast away, she suddenly seems to remember what she was doing and want more? If she had her way, you'd just walk around topless all the time during this time so she could pop on and off all day long and let her interests take her where they will. But of course, it's the rare mom who can do that! Nature knows that they get distracted, so your milk changes; it is likely higher in calories and fat right now than it was a few weeks ago, and your daughter is likely to be sneaking in an extra feeding or two during the day. She may even start night-waking to make up for it (to avoid that, just try to encourage an extra feeding or two toward the end of the day). As long as you ~don't~ supplement, your body and your daughter's body will work together to make sure that she gets what she needs on her schedule. If you supplement, you add a detail that your body can't account for, so it will change the balance.
Of course, there are times when supplementation can be necessary, but they are rare and this really doesn't sound like one. Talk to your ped about what his actual concerns are, is her growth slowing (also bear in mind that a lot of kids' growth slows when you add solids; solids are an inferior source of calories and nutrients, and so their growth will naturally slow, and that's totally ok), and is he recommending supplementation to ease your (or his) concerns or b/c he sees a real medical concern?
Sorry this is so long-winded. The time from about 6-10 months (not that it's four months long, but that it starts somewhere in there for most babies) can be really trying because there are so many changes and they happen so fast, and your ped should know this and be supporting you, not necessarily assuming you want an easy out. That's why this is the time when so many moms give up BF and switch to formula. Stick with it! It gets easy again and your little girl's body will thank you for it!