Baby Dental HELP!

So my daughter just turned 11 months today and we noticed dark dots on her tooth about a couple weeks ago. I took her with me to my dentist appointment so that he can just look and see if it's a cavity, thankfully he said it only a stain. He advised that I have her drink water after every meal and also brush them regularly. We've been doing this religiously ever since. 
Now I notice that the stains are getting worse and the tooth next to it has stains on the back side. I made an appointment with her doctor but thought I'd ask the mothers here if they've come across something like this. I'm soooooo worried she'll have bad teeth for the rest of her life 💔
Note: she's still breastfed and I'm supplementing with formula -similac. I also never give her any juice or added sugar in any of her food. I'm extremely cautious about her food intake, she rarely ever eats store bought baby food, I try to always prepare her food at home. 
Updated photo 👆🏻