Ketones query?

hy guys ,
I am myself type 1 diabetic but i need some info in regards to causes of ketones in urine for my sis.My younger sis has PCOS for which she takes diabex xr she also has hypothyroidism.Now she used to urine frequently and had burning sensation as well during urination but she hasnt lot any significant amount of weight or any other major type 1 diabetes symptoms.We got her OGT(oral glucose tolerance test ) done before she started taking diabex for her PCOS and it was all fine , we did fasting glucose test and it was all fine as well.Recently we suspected she might have UTI(urine tract infection) soe did urine dipstick test and had +1 ketones positive , so thats scared us as she wasnt fasting.Next day i did random glucose test at home and it was fine.So i dunno what else could cause positive ketones ?Any idea and do we need to worry about this as we dont want her to become diabetic or any other health issue?
Regards
Singh