Ok so I had to investigate for my own curiosity after she has exhibited her delusion that she only needs a second seat as a just in case.
So we know Anna is basically the width of her fridge
It appears to be an LG French door fridge, which come in a few sizes as per industry standards:
So let's be really generous and say Anna's fridge is only 30in / 76cm.
Economy airline seats on a Boeing 777 are 17in / 43cm wide, First Class are 21in / 53cm wide. The 777 does long haul flights such as between Dubai and New Zealand.
This seat size chart is missing a bit of data (not sure of what type of seat each column is), but we can see that this chart lists what the passenger width upper limits are plus the hip clearance which is the absolute edge to edge of a seat. The width double & triple are based on the passenger width (not hip clearance), and appears to be a little more generous.
The last column that lists the 21in hip clearance is possibly what a 777 First Class seat is, so a double seat passenger width would be 43.9in / 111cm.
So
standing up, Anna is
at best around 30in across which would never fit into one seat. Now have her sit down and naturally be wider, she would probably be lucky to fit in a double Economy seat.
If Anna is as wide as the widest fridge (36in / 91cm) while standing, she would not fit in a double Economy while sitting but may still fit in a double First Class.
HOWEVER, these seats (premium economy, business, etc) always have a thick divider between which is where the tray table is stored (below is Delta First Class), so it is not possible to spread out across two seats. Some other business class etc. seats on other airlines do go up to around 24in across, but that's it.
So Anna has eaten/drunk herself into only being able to travel in cattle class.