Whilst I'm glad she's been seen happy and well isn't this a giant Fuck You to the Irish Guards that she couldn't even be bothered to send them a well wishes video in place of her absence but instead decides to go shopping. It's one of her (very few) important Royal Engagements of the year.
Nobody is saying she had to attend the St Patrick's Day celebrations in person, or that she was up to it but as their Colonel I don't think a 30 second well wishes video would have been beyond achievable, not unreasonable to ask.
Given she does so little compared to other Royals they really are taking the piss, no?