Cereal has no nutrition in it so your basically feeding her iron which will constipate her pretty badly. My daughter is 14months and barely weights 21lbs EVERYONE tells me she's small but shes in the 50 percentile all she's right where she needs to be. Forcing her to gain weight can cause problems later on. If her doctor isn't worried leave it be if they didn't tell you how to help her gain then she doesnt need to. Childhood obesity is so high so don't force her to gain she will develop just fine at the rate she's going.

Also, you can add more calories to her bottles by making it more concentrated. We had to use neosure which is 22 calories but it's pretty hard on their bellies. You can make a higher calorie count for any kind of formula though!

If her doctor says her weight is fine then it is. Trust me, they will let it be known if they want it higher. My lo is 1 year and weights almost 17lb. He is on the lowest growth curve but finally got there and now hes good. My step sisters 7mo old is 20lb. All babies will be a different weight and will grow at different paces. If you that concerned about her weight, go get a second opinion from another doctor.

Cereal would most likely do the opposite of trying to get her to gain because she wouldn’t be getting as much formula/breastmilk, which is all she needs. Not to mention any type of food isn’t recommended until 6 months old.
How many oz does she get in a day?

If your doctor was concerned he would give you appropriate advice -theres ways to increase calories without risking your childs life or long term gut health. If you're concerned your doctor is wrong- get a second opinion.

Please don’t do cereal it’s a choking hazard. Some babies gain weight slower and that’s fine. My son is on the low end of the growth and weight curve but because he follows his growth and weight curve the doctors aren’t worried. Please don’t over feed your baby just to make it gain weight it’s not healthy

I agree with above. If your doctor who is a trained medical professional isn’t concerned with her weight then I don’t see the issue

All babies are going to be different sizes, you can’t really compare. Does she eat well? Does she have plenty of wet diapers? Her doctor says she’s fine. Nothing wrong with having a petite baby if she’s eating well and wetting enough diapers.
Also cereal in bottles is a huge no-no and choking hazard.

What does her Dr say?