D.K.
Just continue to offer. My daughter had the gag reflex really bad at 6 mos, she finally around 7 mos got solids down and ate well. Some kids it takes a bit longer. My son however was eating solids at 5 mos! :)
Just continue to offer it to her. It is a great time to start her on a bottle too, to free you up, you can pump and then put it in a bottle. That way the transition to sippy won't be so crazy either and she will get the feel of something other then you in her mouth. Just a suggestion.
I think the Dr is overreacting too!! I think give it two mos befor you are concerned but since she is so dependent on the boob, changing up things now will help her a lot as too much dependencey is a hard one when it comes time to wean or offer new things.