Good morning op. I hope you and she are ok this morning.
I have been exactly where you are with a 7 week old (Ds1) and it's so bewildering and you feel so powerless.
Likely they will be hitting dd with antibiotics and antivirals until her bloods come back. Has she had a lumbar puncture now?
Ultimately. DO NOT BLAME YOURSELF FOR ANYTHING! That way madness lies.
Your baby was/is poorly, you have sought medical attention. It is the right thing. You've got a whole childhood of balancing up being with one child and worrying if the other needs you too ahead.
If you have anything like a similar situation to ours, it was all go go go for days, flurries of activity and tests, observations. Then all of a sudden it felt like everything stopped, a brief pause and we were discharged. It felt like the security blanket had been pulled from under us when we were discharged home and I had long lasting paranoia about any high temperature, in any of the children, for a long time afterwards (not helped by Ds1 having ridiculously high temperatures for no apparent reason for the next 4 ish years).
Be aware that baby will be very clingy when all this is over. They are getting used to a lot of passing around and poking and prodding. We weren't able to hold Ds1 for about 3 days until his temperature was sufficiently under control and not spiking. Even though guidance would be not to have pillows at their age, the nurses fashioned him a sort of nest with a couple of pillows and a sheet so he felt like he was being held/hugged and I stayed close by, just stroking his hands or feet, talking and singing to him. It helped calm him and me!