Actually 5-6 oz per bottle is more than most breastfed babies take. The average breastfed baby drinks 25oz of breast milk per day (19-30oz is considered "normal"). So if a baby nurses 8 times they take an average of 3 oz per session (of course sometimes they may take more and sometimes they may take less). Even with 3 bottles and 2-3 nursing sessions that’s about 4-5 oz per bottle. http://www.kellymom.com/bf/pumping/milkcalc.html

However if she's taking 18oz when she is away from you she needs maybe 1-12oz while she is with you. If she's more of a 19oz per day kinda baby she may not be taking very much from you at all, which is bad because her nursing directly should really maintain your supply more than pumping.

It is actually pretty common for caregivers to overfeed breastfed babies. ( http://www.kellymom.com/bf/pumping/milkcalc.html#toomuchlittle  )

Also I forgot to ask, do you pump on your days off to try to bank more milk?

The best thing is to work with the caregiver to find a way for her to take less breastmilk while you are gone, so that you don’t have to pump as much AND she will nurse more when you are around. Was a different person in charge of her the day she did ok on the smaller bottles? If she won't take a pacifier you could try to get the caregiver to give her a clean upside down finger (nail to tongue) to suck on and see if she will take that in lieu of a bottle. Also this has good info for caregivers on how to bottle feed a breastfed baby: http://www.kellymom.com/bf/pumping/bottle-feeding.html  Also make SURE that EVERYONE THERE knows that breastmilk should not be discarded if baby does not finish a bottle, breastmilk is perfectly fine to reheat at least once http://www.kellymom.com/bf/pumping/reusing-expressedmilk.html , if stored at room temp it can be reoffered an unlimited number of times (until the time is up for room temperature storage which is at least 10 hours unless the room is very warm) http://www.kellymom.com/bf/pumping/milkstorage.html  & http://www.llli.org//NB/NBJulAug98p109.html -lists the study that shows a minimum of 10 hours . Also use a low flow nipple and *maybe* one of these bottles though I am not really convinced they are any better: breastflow (http://www.breastflow.co.uk/ (video) US site: http://www.learningcurve.com/breastflow ) or adiri http://bellylaughs.ca/catalog.php?item=9 or http://shop.littlebundles.ca/products/adiri-breast-bottle

Assuming that doesn’t work there are a few schools of thought on this. La Leche League ( http://www.llli.org/llleaderweb/LV/LVDec99Jan00p130.html ) would tell you that a small amount of mashed banana can help tide baby over until mom gets there without stopping baby from nursing when mom does come back. So you could leave 3-4 oz bottles and on the days it isn’t enough give her banana. Not only will banana not fill her up so much she won’t nurse it is far less allergenic than formula (and has no heavy metals). I would also presume it’s cheaper. I know it’s early to start solids BUT adding formula does the same thing to the intestinal pH and flora as solids.
Dr Newman would tell you that its perfectly ok to add water to a baby’s diet as long as it’s not replacing nursing ( http://www.kellymom.com/newman/17feed_baby_working_moms.html ). He would also say that cow’s milk and other solids are fine as well. I am often on yahoo saying to never give a breastfed baby water BUT you are a thinking mom so I would trust you to be smarter than the average person on Yahoo. You could make up bottles that are 4oz breastmilk and 1oz water, that would only give the baby about 3oz of water per day. By mixing it with the milk you are keeping some electrolytes with it. Some experts will tell you that you can give 2-3oz of water between nursing sessions, to 3oz a day is fine ( http://bodyandhealth.canada.com/channel_health_news_details.asp?news_id=4921&news_channel_id=145&channel_id=145&relation_id=0 . http://www.stlouischildrens.org/tabid/88/itemid/166/Water-Intoxication-in-Infants.aspx ) . And of course there was a time when most breastfed babies were given water between feeds and even then water intoxication was rare, though babies may not have grown as fast as they should have. Though kellymom suggests 2oz per day as a maximum: http://www.kellymom.com/nutrition/solids/baby-water.html 

The third school of thought is that “formula is just fine” blech! For the sake of 2-6 oz a few times a week you could make a homemade formula that might be less disgusting? Dr Sear’s is well respected though I’m not sure how good canned goats milk is compared to formula: http://askdrsears.com/html/3/t032401.asp

Of course you could be really radical and find a breastfeeding momma with some extra milk http://health.groups.yahoo.com/group/milkshare/ but of course there are risks to that. If you can get pasteurized breastmilk that of course is safe, but not generally available to non-preemies/special needs babies.

Of the options I would rank it: just giving less breastmilk, water (but less universally accepted), someone else’s milk (if you can find someone you trust), banana, homemade formula, commercial formula. So that’s the end of my book (I really need to know when to shut up)

Brenda