How can i take care of my dogs teeth till i can fix her teeth?

my sister just gave me her dog of 7 years because she knows she can't take care of her any more. the problem is, she hasn't brushed foxy's (the dog) teeth since she got her and her teeth and breath are horrible! I don't have the money to fix her teeth any more because of how bad they are. her front teeth all the way to her canine's (you know the little ones) on the bottom jaw are covered in brown splotches and when i try to brush her teeth they just move with the brush! so i tried brushing her top teeth and her gums started bleeding. what can i do to keep her teeth in some sort of repair while i save up for a doggy dentist?