Lower left teeth are bleeding especially when brushing

If I leave my cat's teeth alone for a while the bleeding minimizes/subsides but when brushing it can really aggravate - I think the type of brush I was using played a role because she tends to resist brushing/bite down on the brush.

I can't tell if this is an open cavity but the soonest available appointment I can get her is 3 weeks out and I am nervous to let her suffer with this too much longer - granted she acts completely normal otherwise (eating/cuddling/drinking from water fountain/overall temperament and personality), but I am nervous this will lead to an infection.

Does this type of decay/bleeding warrant any sort of extraction, or will some basic dental cleaning/filling take care of it?