Client's website text colour changing in dark mode

Hoping to understand something. I have a client's website that has dark text, but when she views it on her phone the text appears white (and it's not legible). She uses her phone on dark mode so I thought it may have something to do with it, but when I test her site on both my Android phone and iPad in dark mode, the text shows in black as it should.

Can anyone shed light on this? Is there anything I can do?

Here's a screenshot on her phone vs on my phone.

Can you share link to page? We can check easier

Sure, the URL is https://www.altitudemovement.com.au