I am going to send a text to her in a minute. Along the lines of "Hi B, hope all is OK today, we didn't know you were off? Thanks for sending over last months £24 for lunch, but as I mentioned on Friday, all lunches will need to be paid upfront from now on. So please can you bring in/transfer the remaining £11 and then make sure you bring some ££ for this Fridays order if you still wish to participate! Thanks x"
Sappy AF! The 'thanks' 'hope you're okay' and 'please'. What the fuck? This person has effectively stolen from you! She owes you money! She is not doing you a favour by paying it back (two weeks late, after you've had to chase and chase her!). Stop pandering to her. It's not rude or confrontational or unkind to be factual. Stop sending her private texts, etc.
Quite honestly, since you know she's going to make a fuss on Friday if you don't buy her a fucking lunch, and you know now she has no intention of settling up her full debt and has basically told you that you will do things her way and pay for her as she is more special than the others, I'd stop doing them altogether because you're a total mug to allow her to pitch a fit so you buy her lunch when she's a cunt who knows exactly what she's playing at.
And HR have advised you to stop them. I think it's really prudent having heard that from them that you stop placing them.
They'll all know it's her, but well, she comes out looking like the twat she is.
'Hi, B. Received £24 from you today. There is, however, still £11 outstanding with is due immediately, I am not in a position to buy lunches for others. As you have my details, I await payment.x'
And then tell the rest of the group there will be no more lunches.
It needs to stop because you know she's going to try to bully you and cause a scene in front of the directors and you have been advised to cut them out.