|Now, if I turn off the DHCP server in it, would it do what she wanted?|
The simple answer is, yes.
First off, reset the unit to factory defaults.
If you google the make/model and something like "make/model manual" or "make/model setup guide" you should find the details on resetting it. Once it's reset, then you can access the management interface and do whatever you want......including disabling DHCP.
I would suggest you click on my name above in this response and read my “how-to” guide titled, “Add a second Router to your LAN”
Pay attention to the scenario wherein you interconnect the two routers "LAN port to LAN port" and configure the second (downstream router) to be part of the network created on the first router. Definitely disable DHCP on it, it's not needed.
Also, I'd have a serious talk with whomever brought the equipment in to your environment without authorization. It could have got you hacked badly.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.