I've tested a few microwaves from different manufacturers with my phone a few years ago. I think I looked at some file in my router (OpenWRT), but I can't recall. I got a lot of dropped packets each time. The amount of degradation was similar for the different microwaves.

I had to put the phone close to the microwave to detect this. The degradation was obviously stronger when the phone was closer.

If your friend experiences noticeable degradation regardless of the distance within the room, it might be worrisome.

But I think it's normal to have some interference. That doesn't necessarily mean enough of the 2.4 GHz radiation escapes the microwave to be harmful to an animal, as Wi-Fi, Bluetooth and so on are very weak, comparatively.

Funny thing is, after putting my phone inside a closed turned off microwave, it got Wi-Fi, although very weak. I didn't try that with all the microwaves, but with 2 or 3 of them.

I think the Faraday cage around the microwave was built to be good enough for safety, but it wasn't built with Wi-Fi interference in mind.

Disclaimer: I might be wrong, as I don't have enough background to make any bold claims.