Could my Dog die? D:?

If your vet truly believed that your dog might die because of this surgery, they would put her down instead of even attempting the surgery, don't worry a bit. I ure you that you have no reason to lose sleep over this. It is wonderful and kind of you to spend the money to remove the tumor and to get her spayed, she will thank you for that. (Frankly, so will your girl puppy...) I will pray for her, and so should you, but it is not necessary, she will be fine.