Drinks round etiquette

[Falsenegative]

I go out with a friend most weeks and have noticed that, on my round, she orders gin and tonic. On her round, she gets herself soda water. I always order vodka and coke. When I first realised I thought she was cheeky, but then I thought, actually, she’s spending the same amount on me regardless of what she orders as I am on her. Another friend, however, thinks she’s BU and it’s very cheeky behaviour.

I know it’ll be suggested that we should stop drinking in a round if it bothers me, but I’m more interested in whether people think it’s acceptable.

YANBU - There’s nothing wrong with her behaviour
YABU - She’s a CF

I wonder if another friend called it cheeky because this way water friend was avoiding to get drunk and kept a clear head whereas OP didn’t .
Some people can’t tolerate others not drinking the same amount. They want everyone to end up equally pissed off.

It makes no difference what a person buys for themselves in a round. How does it affect me? Sometimes people buy a round and don’t even get their own drink because they don’t want one.