Somanynamechanges1 is right.
Unfortunately, this is becoming increasingly commonplace. MATs are pretty much a law unto themselves and, with decreasing budgets and increasing costs, schools are having to make difficult decisions.
I imagine this will mean that the qualified teacher in the year group will have an increased planning and assessment workload as well has having to direct and effectively supervise the unqualified staff member. In this respect, the functional teaching of the children will be ok. The biggest risk is to the impact on recognising emerging misconceptions, recognising the appropriate provision needs of children with SEND and the 'on the spot' changes to the lesson that all teachers make through ongoing 'in the moment' assessment.
Some TAs are brilliant. Others are good. Some adequate and others not so much. I'd hope the school would have put one of their best TAs in the role but that's not great for her and I doubt she's happy either. TA pay is rubbish.
Some TAs go on to become qualified teachers and are brilliant. Others start and realise just how different the role is and leave. So, no, it's not appropriate for a TA to be expected to fulfill the role of class teacher for many reasons.
We had an unqualified teacher at our school for 3 years. She is very good and the school finally trained her but I know that, as happy as she is with that, she is finding the 'extra' that goes with being a qualified teacher is more demanding than she expected.