I tried to gently discuss it with my mum again and she tried to come up with some philosophical BS comment like “life flows like the sea”.
Oh dear.
I find it can really clarify things if you can get people to articulate themselves further, even when it's obvious that's what they're trying to avoid (especially then, really). Again, speaking for myself only, but the way I'd go about it is by finding a way to build on what they said (rather than shutting it down) that nevertheless moves the conversation towards specifics. Like, to that 'life flows' comment, you could say 'that's very true. Help me understand what
you mean by it though, are you saying you think more money will flow your way in time? Or that you think that in five years you'll be content to live on a budget that right now you would hate?'.
I find this works better than pushing back directly. Also, the lure of agreeing and disagreeing with your suggestions can help people take a step away from pure platitudes, which clearly come from just not wanting to think about it too much.
Realistically, you're not going to be able to drastically change their financial course by chatting to them about it. But a looming crisis like this, I wouldn't be able to just shut up about. So I'd just keep mostly nudging, with occasional more srs tough talks, and plenty of private disaster prep!