//"Isn't there an offence "going equipped"//
Yes. Section 25 of the Theft Act 1968. Maximum penalty three years custody.
But this is slightly different. The government has decided that the strategy to beat the virus is to prevent, as far as reasonably practical, close contact between people. contact between people. This is unlike their earlier strategy where they urged people not to go to the pub but thought nothing of them becoming involved in a rugby scrum whilst trying to obtain supplies in a supermarket.
This woman clearly failed the attitude test, which is not very helpful. More than that, she refused to enter a plea in court and almost certainly refused to provide details of her financial means. (I say that because the £811 she was told to pay equates to a fine of £660, a Victim Surcharge of £66 and £85 costs. The guideline fine for the offence is a week and a half's net income and Magistrates work on a default income figure of £440pw when means are unknown).
The difficulty with these restrictions is that there has not been enough time to provide proper guidance. That said there have been reports of ridiculous behaviour in some quarters not only by the police but also by some traders. I've read reports that some shop staff are trying to restrict the goods they sell to "essential" goods despite working in a shop which is categorised as essential under the regulations.