At that height, to be a size zero, my guess would the most that person could weigh is 110 lbs. That’s a whopping 15 lbs less than my 5’3 size 8 aishes chayil. Perhaps of one the other CR folks can shed some light on the weight of a size zero, but figuring on 5 lbs per size, to go from an 8 to a zero, at 5’3, you would need to closer to 97 lbs which would put that person at a 17 BMI (rated as unhealthy on the BMI index)
All around health (mental and physical) should be the goal of today’s people in shidduchim. Not numbers. Read any article about the side effects of axorexia and bulimia, and I can tell you, that is the LAST person you want to marry, especially if your tachlis in life is building klal yisroel (v’hameven, yovin
If you want to talk numbers, make sure they are healthy numbers!