How old is she?
Im 56, and grew up reading children’s books of the Victorian/Edwardian/20s/30s when ‘lazy’ or ‘wasting time’ was the go to insult/parental judgement. It was used for everything; illness, depression, unemployment, creativity without obvious output, political thinking… The books were constantly working to instil industrial obsessiveness in children, usually with a heavy dose of religion on top (Protestant nonsense, you have to read with one eye closed to think that Jesus and the disciples were mainly concerned with putting in 10 hours a day in the office with clean underwear). I laugh when people talk wistfully about some past idyll where children were ‘allowed to be bored’ and were left to get on with things. Maybe in reality they were, but the ideal was nothing like that; see this poem from ‘The Crown of Success’:
‘Lost, one golden hour,
Studded with sixty diamond minutes.
No reward is offered, for it is lost forever.’
I wrote that from memory btw, despite not having read it for thirty years.
So all she’s doing, if she’s around my age, is reflexively judging you with the worst insult her subconscious can come up with. That’s pretty awful and you should push back, but don’t think it’s based on anything factual. Channel the parental end of this interaction; tell her off for being so rude.