We already knew we would teach my son ASL as a baby due to my interest and research showing all of the benefits there are for it during the pre-verbal period. But It turned out to be a life savor for my son who had developmental delays due to his inability to retain weight (long story), but even though he lacked verbal speech he was a rockstar with sign. When I decided to return to work when he was about 2, entirely depending on sign, I knew we had to find somewhere that was willing to sign with him or risk him losing his communication progress.
I know that the situations are entirely different, but we definitely understand the fear of a child feeling left out due to difficult communication. I hope you get things sorted, but I think due to you already noticing, researching, and advocating for her, that you are on top of this and she will thrive. If you feel something is off, listen to your instincts! Don't let people put you in the "overbearing" box. I had friends who would get irritated with me for being worried about my son's development, essentially telling me that I was being too concerned and he would learn to walk and talk whenever he learned... and I had doctors confirming that there were things to worry about! So if anything, make sure you have an understanding support system so you can have a free space to talk about your concerns.
As for sign negatively impacting speech ability, the research that I have done shows the opposite. Bilingualism in and of itself is a major major thumbs up in boosting academics. And sign with speech is an awesome combination for even hearing children (like my son) because it uses both tactile senses and sound to reinforce each other. I know audiologists fear that relying on sign would be a crutch of some sort and negatively impact spoken word, but I would do my own research and listen to what the experts on the other side say. Doctors tend to want to fix, it's their job, so look at the whole picture and see if this situation needs to adapt to her or her to the situation. Everyone is different and there are a million and one ideas of what is right. Look at everything and decide what you think would be best for her. She's an individual and one person's fix isn't necessarily what would be best for her. Your doing awesome though! Sorry this was so long... I tend to talk in circles :/
Aww thank you, I hope your son is doing ok and you managed to find ideal childcare that support him. I am using sign more with her now, she has her appointment Tuesday so going to mention a few things and see what they can reccomend even if they say her hearing is fine