MIDSOMER MURDER

I was thinking recently about Midsomer murders and how in the first series inspector Barnaby had another daughter.
Cully was either still at school or at college and her older sister whose name escapes me was married.
However she had the annoying habit of returning home every time she and her husband had a tiff.
These visits was not well received by Barnaby and were often accompanied by wailing, gnashing of teeth and a good deal of tears.
However now there is only Cully and even she was absent in the last outing.
Does anyone know what happened to the elder daughter?
Maybe Tom could take no more and she's under the patio.
That would be a twist.