Does anyone have any suggestions?

My Great Danes has mastitis again. She has a litter of puppies that are 5 weeks old. When they were a week old she got mastitis. I took her to the vet he put her on antibiotics and we thought that it was all cleared up. Well now the pups are 5 weeks old and she has it again. This time it is really bad and it came on really fast. She was fine on Wednesday and on thursday she was acting a little quiet so I took her temp. It was just a little high so I called the vet and he told me just to watch her and see how it goes. I should say by a little high it was fractions over normal I think it was 102.3 and normal is between 101 and 102. Well Friday morning we got up and her temp had sky rocketed to 105.4. I rushed her to the vet and he gave her a shot of antibiotics and pain killers then sent me home with more antibiotics. She is so sick acting and I guess my question is what am I doing wrong? I asked my vet this and he said that sometime this just happens and there is no way to prevent it. Needless to say she is getting spayed because I will not put her through this again. Has anyone had problem's with this? What am I doing wrong? I thought I was doing everything the way I should but maybe not.