It's a credible theory, plenty of times you see the abductor/murderer send a text to family to buy more time with body disposal and stall the investigation starting, there was one on the Murder on CCTV tv show the other night.
I presume the last text "Claudia" ever sent on that evening has been analysed compared to her other texts to her Mum and others she regularly texted to see if it was in her usual style e.g. sometimes people don't use captials or full stops so interested if there were any discrepancies.
Certainly odd she didn't reply to that Cyprus text that came in around 9pm. Even if she was too tired in the evening, next morning seemed an obvious time. Unless she didn't get the chance by that point.