Little Flower – You sound so much like me not long ago. I have to be honest, as much as I really wished that I could find a clear answer, there just isn't one. Hopefully one of these days the Church will put out an updated guide for modest dress but until then, it is really left up to us. I would say to really try to listen to what God is telling you – as subtle as it, He will guide you correctly. Secondly, what harm is there is suffer a little heat in the summer even if your dress is a little longer than required? But what harm is there in committing a mortal sin if it is just a few inches shorter? … I would say that is you don't know for sure, you should probably err on the side of caution.
Anyway, here are a couple of responses to some of your direct questions – just my opinions.
but if he could read souls, etc, what if this is some sort of "objective" modesty that was revealed to him by God? The reason I'm wondering is because I tend to trust what the Saints say.
We must remember that the Saints were not perfect and were not always accurate. HOWEVER, God did give them do us so that we could work to be more like them and therefore I think it is very important to listen to what they say. I do think there is an element of objective modesty. Take a step back and look at a woman as if you were a man. Look at her clothing – does it show parts of the body that might lead to sexual thoughts/desires?
But could it be, that even what we consider to be modest (ie knees covered is enough), is not entirely modest in reality? what if the standard that St Padre Pio taught - at least 8 inches below the knee, with non transparent stockings, etc, - is what is truly modest? I'm not really sure what to think or how to dress in the world... I already stand out with how I dress just because my skirts are longer.
Yes, I think that perhaps this rule is not the best for our society because of the TYPE of skirts that are worn today. As previously mentioned, a skirt that is longer but thin material, may cause more immodesty that a thicker material. - On a side note, I understand that long skirts are coming back big time. I just went of to Dillard's last week and there were a ton of beautiful and modest skirts. You won't stand out too much longer.
Also, I'm not sure how lose skirts should be.. what is too tight? If it's kind of fitting, but not tight, and then flares out at the bottom, and is long enough, - I don't know if that's okay. I wear A-line skirts but two are like that.
This “mermaid” type skirt in my opinion is not modest. It is very purposely designed to bring attention to the butt and hips. When you put on a skirt, does your panty line show? Any shirts tucked in show? Turn to the side, does the fabric cup you under your bottom? If the answer is “yes” it is too fitted and immodest.
I also read somewhere that sleeves should be at least at the elbow... what happens in the summer when everyone is wearing t-shirts?
This has been a hard one for me but for the most part I can see where this rule comes from. If you look at pictures from the 1910's – 1920's, Women wore sleeves that covered the elbow. However it was part of the flapper style to boy-cut the hair (bob), bring skirt hems up, and for the first time, sleeves showed the elbow. I can see how this can be sensual. I have really noticed that many short sleeves can allow for bra straps to be seen or when women lift their arms you can see into their shirts. You can't really look at the summer time because if women can wear full burquas in the middle east desert in 130+ weather, I think we can manage with a ¾ sleeve in the summer here.
I still have some short sleeves but I am really thinking on phasing them out. However, I know most will disagree with me on this subject but it is just my two cents.