newfoundlands will not thrive nor grow well on food that is not balanced, i hope for your sake her joints and her body grows in a way that it should.
iams is not good food for young growing newfs.
to many people put their faith into their vet.
vets do not know about diet, nutricion and growth rates of the giant breeds, they do not see enough of them, and , it is enough just to keep educated on the medical field
i highly advise you to call your breeder and find out what other foods she recomends, or , you will find, feeding a cheaper food, will not only hit your budget later on thru health issues, it also will lead to more volume in poo.
you also need to contact your breeder, tell her how you are house training ,and ask her for tips.
a breeder should be there to guide you thru the growing stages.
the growth of the first year is so critical, and in my experience, iams is lacking in a lot of ways.