For first injections, give her Calpol before the injection. Make a note of what time yougive it to her.
And buy a digital forehead thermometer if you haven’t got one.
Keep an eye on her temperature afterwards (I won’t disgust you with the story of how we had to use a normal digital thermometer rectally on DD after her jabs, it was a parenting low point).
If she gets a fever take her clothes off and cover her lightly with a thin blanket if she needs comfort. Don’t cool her with water (no longer recommended by the NHS).
Temperatures up to 37.7’ are pretty normal, if it’s higher than that, or you are worried, call 111.
Most babies are fine, just a little grumpy and sleepy. DD reacted quite badly (hence the rectal temperature reading and a trip to A&E... by the time we got there her temperature was normal again...).
She will shout when she has the injection, have bottle/breast/dummy/whatever primed and ready to soothe her.
It feels awful subjecting them to that, butbthey get over the shock almost immediately.