In my experience, like it's been said, rice is the easiest for babies to digest. I would work with that first and foremost, get the little one used to it and make sure she has no reactions to it (allergies). Once she's doing fine on the plain rice, then you can try different grains. They also have fruit flavors available like Rice w/banana and the like, save those for a few weeks to a month down the road and make sure she's digesting the plain stuff first.
I wouldn't recommend cereal in the bottle if you can help it, and no offense, I was just told it can cause ear infections and other results from having to suck harder on the nipple (although if she's breastfeeding, I'm guessing that's not a problem). Make sure to mix it kinda thin (with expressed breastmilk) for the first few times because it can constipate her if it's too thick and she's not ready...
I can go on and on with different things my kids have gone through (2 girls, notice the her/she references) but you will get the idea as time goes by. And NEVER be afriad to call the doctor, that's what they get paid big bucks for
Also, invest in some gas drops, if her belly gets hard or she gets fussy, a few drops may be allshe needs to feel better!!