Mostly I tend to lurk on AIBU threads but couldn't believe the responses that the OP has been given, so thought I'd buck the trend and agree with the OP....
YANBU. I truly can't believe the responses being given to the OP. From all I've read, it's considered normal for an almost-three-year-old to be given licence to scream blue murder whenever she doesn't get something she wants. When, might I ask, is such behaviour 'reasonably' likely to stop (excepting children with SNs)? Would the OP be given the same responses if her friend's DD was 3, 4 or 5? Should the OP continue to have to grit her teeth each time her friend comes over with her screaming toddler? Should she ignore the negative impact that the child is having on her own child?
The consensus of the this thread appears to allow children to behave as they choose, since their behaviour is negated by age. Discipline and boundaries are apparently rendered null and void.
What I find ironic is that in a few years, posters will be creating AIBU threads about the tween and teenage 'yobs' with no respect for authority and no boundaries, yet will be unlikely to connect the lack of discipline as children with such behaviour as they get older. Parents have a responsibility to parent their children and ensure appropriate discipline. Passing the buck by stating that your child is too "bright", or "unruly" to accept such boundaries sounds, frankly, like making excuses to avoid hard work.
I've ceased a friendship with one parent who failed, time and again, to enforce ANY kind of discipline to her DD. Her DD, very bright and very strong willed, was allowed to stand on tables in the middle of restaurants, scream if she wasn't allowed to (this was at the age of 3), punch and slap her baby sister...the list was endless. Her mother, lovely person, sweet and nice, but totally unable or unwilling to do anything to discipline her. Whilst this is an extreme example, it highlights the way in which children's rights and behaviours seem to have trumped those of everyone else. Thinking back 50 years ago, behaviour like that would be unthinkable and parents would be ashamed if their children behaved in such a way.
Yes, some children are more hard work than others, but that doesn't mean that parents should abdicate their responsibilities with flimsy excuses.
So, to the OP, no YANBU!