Part of your issue is that most likely you have the measurement tool attached to the top of her head and the other point on the ground. Hide the ground Crtl-G and with only the figure in view pick a point on her head and the other point on the bottom of her foot. Doing this I can scale La Femme up and down and it doesn't matter if her feet come off the ground. When finished use Ctrl-D to put her feet back on the ground. Now she is whatever height you want in one easy change.

The other issue about scale is a matter of Vendors not building to a reference. Or more likely building to what in theory is the standard and that is V4. She is either 5'10.4" or 6' 3.7" or in simpler numbers 179cm or 192cm. That may seem like a large difference but it really isn't. If all props are built to her and if they reflect real world design so that if say a car was built and V4 got in at the 179cm size she should be sitting with her head close to the ceiling and looking well over the steering wheel. Most short people get in a car and you can barely see their eyes above the steering wheel. SO lets say a car was built to V4 at 179cm then when it is imported into Poser V4 and the car will still look the same as they both scale at the same rate as the numbers are only relative to each other.

The only time this can be an issue is if someone is trying to build something to what they consider to be real world numbers and then put it in the scene with a V4 or La Femme or Pauline (since they within 2cm or each other) and think it is to small because they thing any of the girls above is something like 5'2" 159cm. As long as all objects appear to have the same scale they can be any height you want.

And if it really bugs you make a conversion chart much like inches to metters.

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13