You may also consider increasing the frequency of her brushing. I brush Chloes teeth almost every night (I have missed some here and there) I was sick once and didnt brush her teeth for a full week and there was a bit of gum bleeding. I guess their just like us, if you dont brush often enough you get bleeding gums
I would certainly talk to your vet though as it is very possible as Maximo said that she needs her teeth cleaned. Hopefully its not a bad tooth.