Your MIL can certainly be the hostess. Your only responsibilities are to provide addresses for invitees, show up, and write thank yous. Many also choose to give a gift to the hostess as a thank you.
This is spot on. Mine is being hosted by my mom and MIL and SILs (brother's wife and DH's brother's wife).
All I did was give a list of acceptable dates, confirm the selected date and provide an invite list with addresses. My SIL also insisted I do a registry (but no one has gotten anything from the registry even though invites went out a week ago and the shower is in 3 weeks...I need to find better use of my time than registry stalking...)