@Emmascout1774 (and might as well @RockyRogue1001 in this too), I'm also a teacher and agree with every word you say, also having worked with literally thousands of children.
I never in a million years thought I'd be in the situation where my own DC would not attend school. After all, I've coached so many parents whose children have struggled to attend and said pretty much exactly to them and their young people what you've said in your post above. I've made phone calls and home visits, drafted support plans and made referrals, liaised with EWOs and provided attendance data to the local authority.
Sitting, desperate, 'on the other side of the desk', I find myself in a weird state of cognitive dissonance: I know all the reasons why my DC needs to be in school ‐they should be doing their GCSEs after all‐ but I can not get her there. For years, while young enough to cajole and coax, DC1 did have +97% attendance and we laboured with school and local authority to ensure learning differences were recognised and needs met as per EHCP.
Secondary school has proven quite a different kettle of fish. It has been said that a specialist placement would be more suitable, both in terms of academic attainment and environment, but with zero places in special schools available, we have elected to remain on roll at the local mainstream school rather than 'electively' home educate as ties with local authority support would then be severed. This has taken us down the scary rabbit hole of EBSA and into contact with all the services which I have previously referred other parents to. I'm immensely grateful they exist and are there to keep children and young people safe and on the radar when technically missing in education. But do you know what, all have said, after engaging with our 'case' (being someone's 'case' is alarming in itself) that they've nothing to offer us. They can see we're doing all we can, that DC1 is doing all she can.
So here we are. Not even started the academic year after 12 months of falling attendance. A stalemate with desperate parents, supportive school and a cash-strapped local authority. Our best advice came from CAMHS: stay in it for the long game, keep DC stable and safe, know all is not lost and that there will be options post-16.
@RockyRogue1001, you refer to the law as a blunt instrument. Yet there is provision in DfE attendance guidance for engaging with families whose children's SEN or mental health present barriers to attendance in a much more supportive and responsive way, recognising the individual needs and circumstances of the family as opposed to 'bluntly' pursuing them with fines.
You refer to 'my schools' so I assume you're either an EWO with a caseload of a cluster of schools or some kind of executive head or attendance lead of a MAT, in which case you know that absence for mental health reasons, such as anxiety, can (and should be) recorded as Illness and not as an unauthorised absence, and that parental observation and reporting ought to suffice and no medical evidence is required, eg families should not be required to request sick-notes from their DC's GP in the event of absence.
In cases where there is active parental engagement and evidence of ongoing involvement by external agencies and allied professionals (EP, EHCP, CAMHS etc), schools can assume that a family is trying very hard indeed to comply with attendance expectations and really lean in to support said families instead of referring them for fines and prosecution.