Oh OP
I'm a children's nurse and work on a ward for 0-2 year olds so seeing little babies come in with suspected sepsis is something I'm very familiar with.
Babies go downhill very quickly, one minute they seem fine and the next they aren't. On the plus side though they are also very, very good at bouncing back.
When any young baby presents to us with a fever it is PROTOCOL that sepsis has to be considered and that various tests have to be carried out, including babies. A lot of babies are started on antibiotics very quickly and again that's protocol in case there is an infection brewing not because the doctors all think that the baby has sepsis.
On our ward we treat them as sepsis until we know it's not because we'd rather treat an infection that isn't there than leave an infection to grow whilst tests are done and results are back as that can sometimes take 48 hours.
I have to say that in my experience an absolutely tiny percentage of babies actually do have sepsis or meningitis and it's more often that have a urinary infection or bronchiolitis and that's what causes the temperature.
The fact they don't seem as worried is also a very positive signs because if a baby is septic or meningitic they can deteriorate very quickly and I think you'd be surrounded by doctors.
Please, please don't feel guilty about anything, babies get poorly and identifying a poorly baby is very hard to do in some cases because it's not as if they can tell us they don't feel well.
You acted when her temperature rose...what more could you have done?
You are probably scared and shocked about what's happened but please go easy ok yourself and hopefully you'll both feel a lot brighter in the morning 