Hi N.,
She is defiantly old enough to be off the bottle as most pediatricians recommend you should start weaning your baby off the bottle between the ages of 6 and 9 months.
At first start by putting only water in her bottle. Then try offering her other comfort objects at night such as a favorite blanket or stuffed toy. Try reading to her or rocking her to sleep instead of putting her to bed with out anything at all.
Aim to get the bedtime bottle of milk completely out of your daughters life as you had mentioned it does cause tooth decay. The longer you continue to offer the bottle, the more attached she will become to it, and she wont be able to fall asleep without it.
Only offer the sippy cup during the day and in an area such as the kitchen, or in her high chair. This will help teach her that the sippy cup is only associated with feeding time in the kitchen, or high chair and not for naptime or bedtime.
Always remember to praise your child. You can use phrases such as “who’s mommy’s big girl? YOU, because we drink our milk from our cup“. “Look at mommy’s big girl, drinking from her big girl cup”. “Oh you did it, and drink from the big girl cup”. These all work for potty training too!
Good Luck! Happy smiles to your and your little girl!