She may well be. But if you've had bad times with roms so you don't see them. By your reasoning you would also be racist even if you didn't advertise it
Romanian isn't a race it's a nationality, so that's not really a valid comparison.
However, to do what you describe technically
is prejudice.
I'm not saying there's anything wrong with it, it's justified prejudice to an extent. I would question seeing a Romanian without seeing multiple good reviews myself. After all, a significant amount of the Romanian sex workers are in the UK are trafficked and/or provide shitty service.
But that's still holding a whole nation to that standard, which is obviously never going to be 100% right.
Natalia from Portfolio is Romanian for example, and one of the best providers in Cardiff.
A better comparison would be if I said I'm never seeing a black sex worker due to bad service. It doesn't make any sense whatsoever, because that would include black girls from the UK, from Spain, Africa, Brazil etc. Holding all of those to the same standard obviously wouldn't make any sense, and that's the point here.
People who say she has every right to not see who she doesn't want to are 100% correct, but that doesn't make it not racism. It objectively is.