Hey it was day 45 before I lost my first pound after starting the Keto WOE. Ketostix testing tends to become NEG when on starts burning ketones for fuel but that change over does take varying lengths of time. After 4 years of full time Keto WOE my blood lab results two months ago came back NEG for ketones in my blood work so I am not losing ketones into my urine.

The first 90 days on keto can get weird as we morph from burning mainly glucose to mainly burning ketones. For some it just happens and for others of us not so much. I expect being 63 with failing health 4 years ago was a factor in my case getting weird early on.

I think your advice, along with patience, is the best bet.

As we all know, weight loss has to do with the amount of calories consumed and used, and not with whether you are in ketosis (unless ketones fix a health problem that causes slowed metabolism or ketones reduce your appetite so you eat less). Ketosis is more for health than to move the scale - that's calories.

Perhaps suggest pictures and a tape measure. Sometimes those tell a better and more honest story than the scale does.

My husband has been struggling too, after 9 weeks, he's lost about 9 pounds. He was only eating about 15g/carbs a day and tracking macros with high ketones (I eat up to 50/g day with low ketones and have lost 34).
The issue is that I'm pretty sure he was pre-diabetic. Healing insulin resistance is probably what's going on first (or any other hormonal issues).
The good news? He can wear shirts that he couldn't button a few weeks ago. His face is slimmer. He doesn't need to nap constantly. There are a lot of non-scale things happening even when the numbers don't move.
I did get him to loosen up on the carbs a little one weekend (he ate a cup of chili and a bite of a kid's ice cream) and he lost 1lb a day for the week. Sometimes it works, sometimes it backfires.