The trend now is for employers to not require a degree. It's started to be seen as needlessly discriminatory, unless the job actually needs it.
There's also been research recently that digs into the supposed "graduate premium" and concludes that (as common sense could have told us) it's ability (as measured by A-Levels) and experience that boost earnings, not the degree itself. It's just that people with good A-Levels usually get a degree, so the picture has been blurred. Obviously I'm not talking about degrees like medicine, where the degree is necessary for the job.
If she simply wants to study English and is happy to spend a lot of time and money doing just that, a degree is an option, but remember that nowadays so much of university is online, so it might boil down to a load of online lectures with teenagers and then writing essays in isolation at home. Not an experience I'd pay that sort of money for.
If she wants to earn more, I'd advise she looks at her current £30k admin job, and look around her at the company she's at and other businesses she comes into contact with at work, and think about where she could develop her skills. There's so much she could do, from an admin foundation. She can look at what's in demand, pays well and might be a good fit, and explore what kind of training or experience might get her moving upwards.
I have never considered anyone's degree when hiring, fwiw. Job descriptions used to say "degree expected" or "desirable" but that's starting to be a thing of the past for many business roles.