New rats introduced today and older one acting weird with me

i introduced two young rats today (one is 1 month old and the other is 4 months old). They’ve been together for about 12h hours.

So far between them:
No serious fighting at all
Some grooming (older one grooming the younger)
Occasional squeaks but no injuries or blood
Sometimes they seem calm and even rest or explore normally

But I’ve noticed something with my older rat:
She suddenly became less friendly with me
She doesn’t want to come to me
She seems more easily scared when I approach
She even scratched me when I picked her up trying to escape from my hands (never happened before)
Before today she was more confident, so this change was very sudden.
Is this normal after introducing a new rat?
Could it just be stress/overstimulation?
Any advice would really help, thanks