The first ones who should do something to those (male or female) dressed inappropriately is one of the ushers / whoever is taking on that duty that day. In these days, that's one of the reasons they are there.
The priest would not be expected to see them until they come to the communion rail - at which time he should deny them communion and tell them bluntly, right in front of everyone to leave and not come back until they dress appropriately.
No, I disagree that it should be a male usher. There should be an older lady who's selected for this duty on account of a kind disposition and a good charitable attitude, to point these things out to ladies. When a man comes up to a woman to point out immodest dress, the typical retort is, "so, what? ... are you checking me out, you perv?" That kind of reaction to it, especially if the woman feels embarrassed and humiliated after having been accosted in that manner, is 100% to be expected. You're also putting the male usher into a very awkward position of making it part of their duty to "check out" women as they enter the church. "So you're standing there checking everyone out?" Simply selecting an older lady for this duty completely circuмvents this problem. But, also, the lady should have the right temperament. I've been accosted rudely by male ushers in some Trad churches, scolding me for standing in the wrong place (even though I stand at crowded Sunday Mass because I don't want to take a seat from anyone else, and only after the church starts filling up long after I got there), and I kept thinking to myself that if I had not already been a Traditional Catholic, this would leave a very bad taste in my mouth.
It wouldn't be necessary, either, for this lady to stand in the back checking everyone out as they walked in ... since if someone else happened to notice an immodestly dressed individual, they could go to the old lady and deploy her to take action. :-)
See, the Novus Ordo abuse this notion, but the reason there were "deaconesses" in the early Church were for varoius duties that were not fitting for men to perform, not because they were ordained in any way. So, for instance, Baptism was done by immersion, and often ladies needed some assistance getting dressed and undressed, etc ... and this was delgated to various ladies, these do-called deaconesses.