Of course your mother is right! Don't you know that mothers always know best? How could you even doubt her? I'm afraid you're in for an "I told you so."
Many kinds of birds will come to hummingbird feeders, and house finches and orioles are among the most common after hummingbirds of course. Other birds that you might find testing the sugar water occasionally in mid-Michigan are catbirds, red-bellied woodpeckers and rose breasted grosbeaks. There also might be some migrating birds like warblers that will appreciate quick energy drinks at your hummingbird feeder.
Let your mother know that if the House Finches become a nuisance at her hummingbird feeder she can offer them a dish of nectar for their own use.
Oh and birds aren't the only animals that like sugar water. Some squirrels and raccoons can try the feeders too. And Ken from Green Valley, Arizona took this shot of a Mexican Long-Tongued Bat coming to the hummingbird feeders. These bats are migratory, spending summers in southern Arizona and winters in Mexico. So he sees them in their spring and fall migrations. They are important pollinators of several cacti species.