I wouldn't. They're not doing anything particular at this stage. She's obviously hating school at the moment and why does an illness have to be physical in order to be convincing enough to keep them off. We systematically fail to safeguard our mental health and if she just can't bear to go to school on this one day, let her off.
My kids have the odd 'duvet day' but still have attendance of around 92% which is enough in my book. There are days when, whether it's because of an argument with friends, because they're missing home or just because they're tired and fed up, they really don't want to be in that massive crowd which is school.
Some kids can take it more than others. At one end of the scale some kids are actually school phobic and forcing them to go every single day whatever their stress levels is wrong.
We all know there are large problems with the state school system and our children are feeling the brunt of them. There would be an argument for treating them as herd members before individuals if that herd were perfectly cared for and in a good state but it isn't.
I know this is extreme and possibly not relevant but I have to mention it as it's constantly on my mind.
I have an aquaintance who was asking friends about home ed and very worried as her dd was being bullied and was hating school so much. I told her some stuff about home ed, (she had been told by the school it was illegal ) most others told her not to do it for social reasons. Her dd, as young and beautiful teenager, died in her sleep about a fortnight later. They're still not sure why. The girl had been begging her mum NOT to make her go to school.
A handful of people a year kill themselves because of bullying. There must be thousands more who are under terrible stress but we don't hear about them.
We MUST listen to kids when they are stressed about school and not have this blanket blinkered 'send them anyway to sort out the issues themselves' approach.
We're making them go to school. We must be responsible enough to be aware of their stress levels and not be so dogged that they feel they're abandoned by home, into school, daily, come what may.