A lot of people are unfortunately VERY misinformed about this, you dont know how many times I have heard this myself from people who see me OC. The truth is a CPL gives you the ability to conceal but it does not require that you conceal. Early on even police officers were telling people that a CPL meant that a firearm HAD to be concealed, some probably still are, however that is not the case. You do not forfeit your ability to OC.
What you read in MSP update #86 is correct, someone with a CPL can openly carry a firearm in the state of Michigan as well as in the pistol free zones as MCL 28.425o only concerns the carrying of a CONCEALED pistol.
What I would do (since she suggested you look up MSP #86 from how you make it sound) is take a copy of MSP #86 into them so they can read it.
What the case may be is they are VERY unknowledgable about the laws as we have them today and the understanding of them, or they are very anti open carry and are trying to push their agenda onto you so that you dont know any better.