How about I am not comfortable with you touching his penis at all. Since I have read up on proper care. So please just dont touch it.
Honestly mama if you see what damage can be done by this type of thing you wouldnt hesitate to say something.
I suck at confrontation but after seeing my ds hurt not once but twice by this I finally said enough and even though my face was bright red and my heart was threatening to jump out of my chest I refused to allow the Dr. to even touch my ds's penis. I moved it around for him (not the foreskin the whole penis)
Your ds could be hurt by this so treat it like you would anything else that might hurt him that you can prevent just do it.
The foreskin is definatly reseliant but why risk it IYKWIM?
Not to mention her doing this more than likely she will eventually start to "worry" because he is X age and isnt fully retractable. When in fact there is no set age for retraction to happen. But hearing a Dr. say your ds has a problem is more than likely going to scare you with no reason.
Yeah this one is where you need to grow a pair

You can of course just not allow under the diaper checks at all. It is your choice.