I have a year 9 daughter as well, and it is hard - the first couple of weeks locked down she didn't want to do much at all. A straight honest discussion about losing her allowance, her phone and her internet soon resolved a few issues.
You have to put a different perspective on this if you can. I - like you have a full time job, I am currently working from home and trying to manage the school work for a year 9, a year 1 and a nursery child. They have to do at least 2 hours a day, they can split it up if they like but I check they've done it and I help the two little ones upload theirs. Then they can have their tablets/phone.
I also throw them in the garden after lunch for half an hours exercise (weather permitting).
Its not anything like what they'd get in school but as parents we have to own this time. Everyone is doing what they need to in order to get by but you don't want to raise children who just give up because things are a bit tough. If you're struggling with motivating her for a few weeks, imagine how hard her teachers must work with her on a daily basis in school.
Its true - many kids will be in the same boat when school resumes, but I would like to think all kids are doing something productive at home, whether its the designated school work, reading, being creative, doing DIY projects - anything that is still keeping their brains busy.
I do worry sometimes that some kids will go back having done all the work that has been sent home, and then will have to re-cover it all in class because other kids haven't. There are lots of reasons why this could happen, most of them are very valid but I don't personally feel that giving up because its hard work is one of them.