We're in a similar situation. We just found out last Thursday that Poofters has mammary lumps. Our vet isn't sure if they're tumors or cysts, so this Tuesday she'll do an ultrasound to determine what they are, so if they're tumors she'll do surgery the same day, and if they're fluid-filled cysts she'll aspirate because they're so close to the surface. Poofters was spayed in January because she had ovarian cysts that were growing rapidly. She came through the surgery so well that I feel fairly confident, but it's still somewhat stressful. I'm doing all the things necessary to prepare for surgery, but of course I'm hoping she won't need it. Like Cupcake she's otherwise in excellent health.
How is Cupcake now? Have you had the surgery. All the best to you!