There could be a couple things going on. The Black Spots could be what is called Black Spot fungus. It's attack upon the rosebush is stressing her out, thus she is using all her energy to fight the infection and thus not blooming. Spray the rosebush with a Fungicide that is listed to get rid of Black Spot, such as one called Mancozeb. It is available thru Amazon.com. The other issue could be the pot. The rosebush may not be happy in the pot due to it being too small and/or perhaps does not have good drainage. In this case, I recommend transplanting the rosebush to a new larger pot that does have good drainage holes in it and some good soils for drainage to fill in around her in the new pot. Once transplanted into new pot, or garden, water her in with some water that has a product called Super Thrive in it along with a Root Stimulator product in it. I use Fertilome Root Stimulator. Water her with a fresh batch of the noted double product water mix the next 5 times she needs watering. Also give her a little kelp meal (1/3 cup), mix into the soils a bit and water it in. That makes roses happy. :)
