Taylor Swift is good for beginner songs, but very wordy, so that’s the trade-off.
Valerie (Amy Winehouse) is upbeat and fair easy.
I’m like a bird by Nelly Furtado only goes up to Bflat and is fairly speaky.
Royals by Lorde is fairly straightforward and low too.
Somewhere only we know (lily allen did a version of this from memory)
Let it be by the beatles it pretty simple and doesn’t have a huge range if you can put it in a key that suits the student
Same with yellow by coldplay.
Most things by oasis (wonderwall or don’t look back in anger, both dead simple)
Under the bridge – red hot chilli peppers
Other side – david gray
Four seasons in one day – crowded house
A few ideas to get started with at least 🙂