That's not what the article says.
It was only after Sara died that a schoolfriend told her mother she came to school with visible injuries, claimed they were from falling off a bike, and the next day she left to be homeschooled. We don't know if this explanation was accepted by teachers or not.
We do know that Sara was 'known to social services' and the police. Social services won't comment further at this stage. We don't know why she was known to social services, or when a report had last been made. It could have been years prior; her parents seem to have gone through a messy relationship breakdown with mum not allowed access for the last 4 years. The police described their interaction with the family as being "limited and historic" so her recent situation appears to have been entirely off the police's radar.
One neighbour seems to have taken an interest in Sara's welfare, and I rather doubt this was welcome. Her dad appears to have told a neighbour a story designed to make her think that home education was in Sara's best interests, and therefore get the neighbour off his back. No one else seems to mention bullying.
Indeed, the timing of the facial injuries and her removal from school the next day make it seem highly likely that she was removed in order to keep her out of sight of teachers who might start to question the falling off a bike story. 5 months later she was dead.
Fundamentally, children who are in school have an opportunity each and every day to see a trusted adult who they could disclose abuse to, and who could notice that something isn't quite right. Home educated children don't have that, or anything really.
The nice middle class parents who want to teach maths through baking cakes, read to their children every day and use InterHigh seem wilfully ignorant of the very real safeguarding issues that crop up in some families, and loudly oppose any form of regulation or inspection for home educators in case it inconveniences them. Putting their convenience over the lives of children like Sara, Dylan and Khyra displays a stunning sense of selfishness.