Re:PWS and Height?
My daughter with facial pws is of average height at 17 months, but our 2y8m daughter is also as tall as a 4 yo (her brother), so it may just be in the genes. You are more likely to notice that where your daughter's pws is on her face that is may look slightly larger than areas without pws. I have noticed that on Claire. Her right side (pws side) looks bigger (but not huge that other people seem to notice) than the left side, that has a small light pws up her cheek bone.
Hope this helps and all the best to you and your daughter.