The Sassy Mam Ultivent Bottles are the best for breastfed babies in my opinion - the nipple is flatter, like the breast's nipple gets in their mouths, and they have an anti-gassiness vent in the bottom - you can find them at Walmart.com http://www.walmart.com/catalog/product.do?product_id=1020... , and eBay. My two mainly breastfed babies just messed around with regular cylindrical nipples, biting them, droolng their meal all over themselves, sticking them in the corner of their mouth like a stogie LOL! These nipples they don't miss a drop, and usually only have to burp once per feeding!
Also, although they don't "seat" or snap in to the ring of a playtex "bag" nurser, these nipples will work with that system, (I do like those bottles for the non-washing convenience) you just sit the nipple on top of the bag/bottle assembly, and then screw the ring down tightly on top. If you are going to pump, "the first years" make a breastmilk storage bag that will go right in the playtex bottles, and playtex itself has a system (if you have their pump) that goes straight from pump to freezer to the bottle itself.
Also, have someone other than you teach them to bottle feed, you may have to be totally out of the house for it to work at first, especailly starting this late, they will usually not eat a bottle for mommy at the beginning, since they prefer the real thing if it is available. Probably best to start withthe bottle with breastmilk only if that is all she has ever had, formula is going to taste yucky to her - use breastmilk to teach her to use the bottle, then gradually mix it with formula, first a little formula with lots of breasmilk, and then up the formula and lower the breastmilk, every few days, until you get to where it is all formula. Pumping would be much less expensive, though, and must be allowed by law BTW, just FYI, it can cost between $1800-$4000 for a year's worth of formula (depending on how much the baby eats and what brand you go with).
Whatever you decide, good luck - and those Mam bottles are wonderful!
Jessie