L.F.
Your baby is just smart...she knows what she likes and that is the breast. Even though she prefers the breast over the bottle you might try these tips, which you may already know, to get her to also take the bottle. 1)Have someone other than yourself give her the bottle and you stay back while they do it so she's not smelling you and wanting Mommy. 2)Give her the bottle more often and pump milk to give her in the bottle (formula tastes different and is not as sweet as breastmilk) or pump to put in reserve so your milk supply doesn't diminish. 3)Try a different bottle. We always did great with Avent bottles and nipples but my sister's baby preferred Dr. Brown bottles. 4)Seek out a breastfeeding support group that you can get more individual support from other mothers who are currently going through the same things as you, it may help your sanity and give you the encouragement you need to stick with it.
They grow up fast so enjoy your baby and breastfeeding while you can and don't stop or wean your little girl until you're ready. Each child is different. I breastfeed my 1st child for 14 months and when my 2nd came along I thought 'No problem'...I'm a seasoned Mom cause I've successfully done it before but my son had an immature suck and gave me red, sore nipples with pain like needles. I ended up going to a lactation consultant and I stuck with it...it got better and he nursed until 12 months. I've also nursed my two littlest girls as well. It is a blessing! Best wishes!