Unless the girl in question is under 5 ft tall, I’m willing to bet a size 0 puts her in the unhealthy category.
If she’s of average height (figure 5.5 or so) her size had better be closer 4 or a 6.
Wanna drive the shadchan nuts? Ask her what the girls BMI is (20 is ideal). If the Shadchan says, what’s a BMI?, if safe to assume the shadchan is probably a size 18 herself, so who is she to throw stones? (if its male shadchan, size 18 would be 46-48 REG)
In short, its not the dress size you’re marriying, its the person. Health matters more than appearences. And on the topic, it would not hurt us CR dwellers to google BMI and see where we rank. Health matters to all of us!