My partner has been working on spike proteins similar to the Covid ones for years. Although his work isn't directly connected with how long people are infectious, he does keep in touch with the research.
So ... to answer the op's question about whether she is still infectious, I'm linking to this article. I ran it past my partner, who agreed it seemed sound, and it's written in layman's language, so even a non-scientific person like me can understand.
www.nature.com/articles/d41586-022-02026-x
It confirms very much what most people know. Covid is most infectious in the first few days, but it can be infectious for longer, although it's rare for people to be infectious beyond 10 days.
In that context, the government advice is probably about right. Try to isolate for five days after a positive result but if you want to avoid infecting anybody who is particularly vulnerable, you should stay away for 10 days. I would include any medical setting as a place where there are likely to be vulnerable people.
Personally, I have a particular reason to not want to be infected in the next week, so I'm going to stay at home when possible and wear a mask if I do have to pop out to a shop. I can't rely on other people using their "common sense", I'm afraid. As far as I know, I haven't had Covid so far.