S.T.
This is kind of long - sorry about that.
My daughter is slow to gain, but doesn't LOSE weight. She has always been in the 25th percentile for weight and the 75th for height. I think either at her 9 month appt, she had gained only 4 ounces, and my pediatrician wasn't really concerned due to the fact she was still growing. Sometimes as they grow, it doesn't show up as weight but as length. Just keep tabs on it and if you ever feel like taking her back to the pediatrician or calling their office, never hesitate. You can often just take your daughter to their office to weigh her in between check-ups if you would like - to keep up more closely. My daughter is now 2 (26 months) and weighs about 23 pounds - there are friends of hers that are 9 months old that almost weigh that! :) Know that kiddos have ups and downs regarding their weight gain and growth. I am sure everything is fine.
My daughter didn't love the taste of cereal either - so I mixed in baby applesauce to make it sweeter. Now that your little one is six months, it's okay to start to add food to her diet (baby food, that is). It may help fulfill her food need and help her to gain some weight as well. You don't have to stop the breast milk - she still will need to, and I am sure want to drink that!
I started the majority of the baby food for her as veggies along side cereal or applesauce. Once she got the hang of it, I introduced fruits. I had heard that if you start with veggies, they will eat them - if you start with fruit, they sometimes won't eat veggies. If she doesn't like the veggies, try what I did. I dipped the spoon into the veggies first, then dipped it into the fruit. It was kind of disguising the veggies, but my daughter ate them both that way! Be careful about giving your daughter berries or strawberry fruit blend baby food - they say to hold off on that due to potential allergies. The veggies my daughter loved were squash, sweet potatoes, and green beans. She hated the peas and still won't eat them! She loved the banana baby food, the applesauce, and some of the fruit desserts (guava, banana blends, etc.) Also, try to feed her baby food first, then follow up with breast milk. That way she'll eat more "food" and then drink what she needs. During the night she can get just breast milk, and probably first thing in the morning too.
The day care may also have better luck feeding your daughter food - communicate your concerns about her weight gain and how you'd like for them to do the feeding If you find a routine to feeding that works (like I did), ask them to do the same thing at daycare.
Lastly, and my advice always, talk with your pediatrician. If he or she is concerned about the weight gain, then ask what things they recommend you try. If they are not particularly concerned at this time, just try to introduce some baby food and see what happens.
Good luck - we moms worry about everything, and we make ourselves crazy about it. I am sure you'll get some great advice, these are just some of my thoughts.