Teachers Contracts

Good morning I am new to working within a secondary school. I have. A teacher on a 0.47 permanent contract. She has done a variant on average of 0.33 making her 0.80 contract for the last 10 years. At what point does this make her full time hours. Has anyone come across this? What if she is entitled to a full time contract would this not open up other teachers looking at their contracts and stating they are entitled to up their contracts. Thank you