Except for their CEO's support of the US Republican Party!
But more seriously, you might want to check their FAQ on https://protonvpn.com/streaming which implies that using it to watch SBS's Australia-only shows isn't legal, unless you're normally resident in Australia. Proton also lists "Infringing upon or violating the intellectual property rights of the Company or a third party" in their terms as unauthorized use, and I suspect Warner Bros would say this is infringing on the exclusive UK rights they've spent quite a bit of time and money amassing, so your wife's account can be restricted, suspended or terminated if anyone notices.
So far, it seems that it's not happening much, but I'd be aware it could and think about how you'd deal with any potential difficulties account suspension could cause you or your wife. I suspect we won't see it happen in 2025, at least not until after the last free-to-air Tour de France, but once TdF and Paris-Nice highlights are TNT-only, the heavies may start working people over.