Immigrationboards.com

Hi

my sister is an EU citizen she submitted her appllication online and is waiting for the reply email where she is invited for biometrics.

Can she travel outside the UK and come back for the biometrics?

thank you

Yes travel is allowed - naturalisation is not an immigration application.
Ideally it's best to get biometrics done before travelling to avoid any delays just in case.

Some people wait months to do biometrics so she can do when she gets back.