OP says they are a qualified teacher so I was wondering why she doesn't work as a teacher if she's just going to get roped into doing the job of a teacher
I can answer that for myself not the OP.
I do Cover supervision, at half the supply rates, because I want:
a) a job where I go in, get on, get out
b) school/child-friendly hours as I am a single parent
c) delivering lessons only as planning and marking will mean I can't lone parent two ND kids of my own very well
d) regular hours/school as Supply unpredictable
e) same school so that I can make positive relationships
If I was a HLTA expecting the bulk of my job to be 1-1 interventions, that's a very different job to what I do. Cover is Performance/Delivery/Classroom management. It's akin to doing stand-up with an unpredictable audience.
I only do it for the reasons above.
If I was the OP with a different job spec but being hammered for cover, every time a teacher was out, that would get on my tits. Just because they can use her, doesn't mean that they should.
They are, because it is cheaper, the kids know her already, they'll probably get more work done.
I think it would be fair, that even without marking or prepping, she got at least M1 daily rate/or the lowest they'd pay an agency excluding the agency fee - because day-to-day supply do not prep or mark either. The only reason I don't do that gig anymore is that it is unstable and you feel like a ho, being pimped out by your agency, who sometimes lie to both parties about what they're getting.
In your shoes, OP, I'd count how many teacher days you've done over the past two terms and point out what they have saved and what % of the job you applied for, you actually do.
I am not returning to teaching full-time with all that that entails.
I do know that what I do, I get around £65-70/day for. Supply sometimes get double that and are not as good as me. Them there's the breaks.
I have been asked to actually have classes though when no teacher. Not meant to do longer than two weeks (union)/known absence/proper vacancy.
I grew a pair and insisted on M1 for a % of my week as once you take a class, even with a set scheme of work and little planning, you still have the ball ache of assessment, marking and data input. If it's not in your job description, you shouldn't be doing it without extra remuneration. If it is in your job description but they are taking the piss m ore often than they're not, you need to be prepared to walk or see your union rep.