‘mais je suis arrivée un peu plus tard’

Hi Judy,

The English actually says-

'Yes, but I arrived a bit late' = 'Oui, mais je suis arrivée un peu en retard' 

and as the previous sentence had 'there' in it -

'And you, were you there?' = 'Et toi, tu étais là? '

There/y although grammatically correct would be totally superfluous ...

Hope this helps!