My first reaction to this is to think you must be seeing the wrong ladies! I find it very shocking that any lady would have this issue, but I guess some things can cause it.
What I would do, is one of two things.
1. Which may not be the more popular option. BE BLUNT . I, personally, would prefer this. Tell her about the issue in a blunt but kind way. If I had this issue I would want to know.
2. If one is not your style, tell her that showering together is a huge turn on. You can easily clean the lower regions without messing up hair and make up tell her you want to get her all wet and have fun with it.
3. Another option which I wouldn't recommend so highly, bring scented/flavored lube and use it. Like I said, I don't really recommend this because it is just putting a bandaid on the problem .
There is one thing that some may not know, LADIES DO NOT EVER USE REGULAR SOAP ON YOUR CHA CHA. It throws off you natural PH balance and no matter how clean you are, you will retain an odor it doesn't happen to everyone, BUT if you are showering multiple times a day and using soap down there in between it is highly likely. And once it starts you need antibiotics to fix. Buy the special soap for ladies parts OR washing thoroughly with only water will do a fabulous job!
I hope this helps!