Is Emma flirting or is this a younger sister teasing an older brother?

The age gap and the family relationship both can make this a little icky - though people talk about it less than Marianne and Colonel Brandon in Sense and Sensibility

Michael McCarthy. (2021, August 27). #COVD19 vax rates are still increasing in Australia. The over 70s are approaching 90% with first doses. The red line is the rate for all people >=16. That should reach 60% soon. Https://t.co/NH3Q7jumgT [Tweet]. @mickresearch. https://twitter.com/mickresearch/status/1431185640884826112

Niet, A. de, Waanders, B. L., & Walraven, I. (n.d.). The role of children in the transmission of mild SARS-CoV-2 infection. Acta Paediatrica, n/a(n/a). https://doi.org/10.1111/apa.15310