What amount of funds does my Thai girlfriend need to show for her UK Standard Visitor Visa application?

Question: We are trying to plan for my Thai girlfriend to visit the UK for for the first time, for a short period, probably in the region of 5 days, plus a 7 day cruise to the Norwegian Fjords sandwiched in the middle. She has done group/family travel to the Schengen Zone a couple of times without any visa issues. In an attempt to get the UK Standard Visitor Visa application to go through smoothly, what kind of amount of funds does she need to prove to have in her bank account to satisfy UK immigration requirement for the visa application, bearing in mind she will only be in the UK for about 5 days on this first visit?

Return flight ticket, accommodation booked, having a educated and decent job, own house, family commitments, never overstayed anywhere, seems to tick most other boxes to satisfy the application. Just needing an idea of the amount of funds in her account that she will need to show, to allow the application to go smoothly