Toddler teeth gray marks?

UPDATE: The tooth turned completely grey-greenish. The dentist did xrays and confirmed she had badly injured her tooth at some point. Not decay/rotted. The dentist said this is very common in toddlers and an injured tooth can show up years after the fact, she could have injured it a long time ago or recently. She ended developing an abscess in the gum line just above the tooth. This prompted the dentist to remove the tooth. Her adult tooth will not come early, it will come in later as she gets older like normal. So for now we have a toddler missing a front tooth for a few years and she is happy as can be!

My almost 3yr old developed these gray marks on her teeth, I just noticed a few days ago. They do not come off. Im freaking out! Im not the best with brushing her teeth BUT we do try to be regular with it. She is not allowed to drink juice or pop. Milk or water ONLY.

She grinds her teeth REALLY hard at night and is also on a prescribed liquid iron supplement.

Her nana babysits and often gives her treats including candy😡 and flavored water. Im going to call the Dentist Monday, but Im freaking out and never seen this before!

Also, I know her tonsils are huge, she has surgery next month to remove them.