TL:DR - Nothing looks wrong, get them to clear their cache or use incognito.
I can’t seem to replicate the issue I have even opened in inspect and used the device toolbar to see if that makes any difference. Do you have a link to the published site? That might help with the inspect device toolbar.
From what I can see it is pretty fluid. When selecting the different viewports at the top [Desktop, Tablet, Mobile Landscape, Mobile Portrait] there is a slider along the side of the demo which allows you to stretch and compress depending on the device and along the bottom there is a ruler which shows which devices are at which size (Handy tip if you didn’t know). All along they seem to be fine as well.
I would recommend that your client/friend opens up an incognito tab on her device as she maybe experiencing caching issues.