Indoor or outdoor?
NWI has a wealth of banquet halls - it's actually kind of strange really.
Probably the most unique place is Meyers Castle in Dyer - but I've heard some not so great things too ... overall cleanliness, their insistance on their in-house vendors, not getting what you pay for (paid for roses, got carnations), etc.
There's also the Marquette Park Pavillion which is right on the beach in Miller.
The Barn at County Line Orchard in Hobart.
Other than those, here's a list of the "typical" banquet halls if she decides to focus her search on those:
Halls of St. George, Schererville
Villa Cesare, Schererville
Andorra, Schererville
Teibels, Schererville
Patrician, Schereville
St. George, Schererville
Avalon Manor, Merrillville
Radisson, Merrillville
Engineer's Hall, Merrillville
Croatian Center, Merrillville
St. Elijah's, Merrillville
Hellenic Cultural Center, Merrillville
Banquet On The Green, Merrillville
Promendade Hall, Merrillville
Innsbrook Country Club, Merrillville
The Patio, Merrillville
Casa Maria, Dyer
Duneland Falls, Portage
Woodland Park, Portage
River Pointe Country Club, Hobart
Ambassador Banquets, Hobart
Dynasty Banquets, Hammond
The Center at Purdue, Hammond
Chetnik's Memorial Hall, Crown Point
Crown Point Courthouse, Crown Point
White Hawk Country Club, Crown Point
Wicker Park, Highland
Cloister In The Woods, Munster
Center For Performing Arts, Munster
Sand Creek Country Club, Chesterton
Waterbird, Chesterton
Strongbow Inn, Valparaiso
Legacy, Valparaiso
Aberdeen, Valparaiso
Old Town Banquets, Valparaiso
Casa Roma, Valparaiso