You need to keep a very close watch over her teats- mastitis usually shows up with engorged teats becoming warm and red. In the past I have had to express-gently- milk from teats that look suspect then massage with a warm damp face cloth-hope that helps a bit! Good luck.
Expressing milk really works - and keep rotating the puppy onto different teats so that they all get a chance to be drained. Milk supply seems to be up and down the first few days but then it should adjust itself. Try not to be tempted to bottle feed as the bitch needs chance to self-regulate her milk flow.
We were given antibiotics with our last c-section but to be honest it gave the puppies terrible stools but you need to keep a close eye on her - I usually take mine at 3 days when I have dew claws done for a quick check over, then again when going back for stitches out.
I know it's a worrying time, make sure she is getting out for a wee and poo
and that everything is working as it should
Put the puppy on the biggest/hardest teats and persevere - Good Luck!