Normally, if you jump down a ladder and try to look up Ashley's skirt, she will grab it and call you a pervert. However, there is a location where she does not do this. In Chapter 2-3, go to the lifts, after going down one of the paths. Climb onto one and go all the way down to the other side, shooting the Gonadas coming up on other lifts and the ones on the platforms. Once you get all the way down, go down the stairs nearby. Go to the cave that is here that has window-like holes. Be careful, as there are two dynamite wielding Gonadas at the entrance. Kill them then jump over the wall and go up the ladder. Kill the Gonada. Jump down, but leave Ashely up there. Try looking up her skirt with a sniper. She will not grab her skirt and call you a pervert because she is too high up. There are more ladders where you can do this. Find one with a large drop and it should work. For example, if you have already gotten past Chapter 2-3, you can do this trick on the ladder you go down just after defeat Saddler in the final chapter.
After you defeat Ramon Salazar, walk further and there will be an intermission sequence where Ada will ask Leon if he needs a ride, and he accepts. When Ada brings him to the island, she will hook a rope onto the top of a cliff and say" I have some business to take care of". While she is saying that, look at her skirt (especially when she goes to jump up). You can also see more of Ashley than usual when you jump out the window of the church and when you get on the jet ski.