Ruby-throated Hummingbirds have mostly grayish flanks rather than coppery like Rufous Hummingbirds. https://www.allaboutbirds.org/guide/Rufous_Hummingbird/species-compare/#:~:text=Ruby%2Dthroated%20Hummingbird-,Female,Rufous%20in%20western%20North%20America.
The female Rufous and Ruby-throated look very similar to me. The only way that I can tell them apart is the Rufous looks like it has a brown vest on.
IN MY VIEWFINDER 
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