No. NO! Prutza is NOT appropriate. These women are usually NOT bad enough to warrant the term “prutza.” A skirt that covers while walking and standing does NOT deserve to be called pritzusdik.
I have a sister-in-law who was OTD for a while, and now b”H is back on track. She dresses VERY differently than her mother and sisters (and SILs) – her collarbone is not always covered, some skirts are too short (and some may consider others too long), and she sometimes doesn’t wear socks or cover her elbows. I can guarantee you that if someone were to approach her and tell her that she is not dressed appropriately, it would cause her to have a major setback. Her family and friends are just grateful that she is keeping Shabbos and other mitzvos. She is one of the strongest people I know, and I admire her greatly. I would never DARE tell her that she is not tznius, and I’m family!
While we have a chiyuv of tochacha, we still need to know when it is appropriate to give tochacha and when to keep your mouth shut. It is simply NOT appropriate and most likely harmful to tell a perfect stranger that their skirt is too short. I would rather have to give a din v’cheshbon for not giving tochacha than for turning someone further off, causing her to dress less tznius, or making her go off the derech. NOT okay.