It just sounds wrong. It's not a real word. When the girl in the video says Britishly, I thought she was crazy or just playing around. I did a search on Google and it looks like Britishy is a real word. It's in an online dictionary . And a couple of major websites have used the word. I was shocked to learn it was a real word. Spelling and grammar are not my best skills. Maybe it's just me, maybe I am the only one who has a problem with the word. I don't care if I am the only one. I don't care if it's in an online dictionary. It just sounds wrong. You use the word British not Britishly.
This is the definition from the online dictionary. LINK
Definition of BRITISHLY
: in a British way ( a Britishly calm bystander )
A Britishly calm bystander? It sounds wrong and weird.
Her YouTube Vlog channel