Totally with the lady.
Once out at a Chinese restaurant, not drinking as I was a designated driver, I had ‘the vegetarian special Set meal’, which was £21 including a soft drink (more with alcohol). Apart from the other designated driver, everyone else had quite a lot of alcohol, extra portions of things, more alcohol, pudding, coffee etc. The 11 way split was £39 and change per person.
I stuck to my guns and said £21 was all I was paying. When the furore began I suggested that I put my £21 in the pile and went home and anyone in my car who argued with me could walk home, or get a cab/bus or rickshaw for all I cared. The other driver quickly totted up his meal and his wasn’t that much more than mine and took my side. There was much grumbling on the way back about cheap nights out, not paying way etc
Why should anyone pay a vast amount more when bill splitting? If it’s a close call, all well and fine, if a vast discrepancy, it’s unfair.
Just to add, I put money in the tip tin on the way out. I didn’t want to shortchange the waiting staff.