How much does she want to change it?

Looks like it's varnished already. You might be able to darken it slightly with a couple more coats of that.

Otherwise you will need to strip back to bare timber to stain.

I've not used this myself, but Resene also has a whitewash/greywash product that says it can be applied over existing varnish (though you will still need to sand back to a dull finish, that is a heck of a lot easier than right back to bare timber). See https://www.resene.co.nz/comn/whtsnew/go_white.htm and https://www.resene.co.nz/archspec/datasheets/d50W-Colorwood-Whitewash.pdf 

You could sand it back and Danish oil it. Gives just a bit of a darken without loosing any grain. Takes about three coats, I like to rub it on with a soft cotton, lint free cloth. Old cut up cotton t shirts or sheets are ideal. You want thin layers and a fine sand I think between coats (it's been a while).

Flip it upside down and try a spot on the underside before committing to anything whatever the decision is.