Help me and my wife!

[ATL_Gator]

I need help dealing with my wife with the suggestions I am giving her regarding weight loss. Helping her is getting past this stupid plateau. Helping me is keeping my sanity.

History:
Since the beginning of the year, my wife has dropped 45 or so lb. She is still 15 lb or so from her goal weight. (she is doing fantastic, by the way). Her strategy from the start, per my suggestions, was calorie control. She can eat what ever she wants, so long as she stays with her calorie goals. For 4 months or so, that was it. After a while I convinced her to "up the activity" some. Not a crazy amount, but some. When she is at work, she has an active job on her feet all day. On days where she doesn't work, she has started walking. No weights, no strenuous activity.

When she started, I calculated her BMR, for her weight at the time (1600) and for her goal weight (1350). Based on that info (and before I could go any further), she set 1200 calories a day as her target.

She sticks to it. And not net calories either (accounting for activity)... 1200 calories eaten or less. EVERY now and again she will go over, but that has been easily a month or longer ago. "Go over" is about BMR of her goal weight, so she should still be under maintenance.

NOW, the problem:
From the beginning of the year until about 3 weeks ago, she was seeing consistent weight loss. She had a small plateau at 150 for a week or so, but that was it. The last 3 weeks she is stuck. She only goes by scale weight as measure. The last three weeks she has been between 143 and 147 (which was today, and delivered with a lot of complaining). She is getting frustrated, and bugging me.

Why am I not losing any more weight? Still eating at or below 1200 calories per day, per MyFitnessPal android app.

I tell her "it's just a plateau, keep doing what you are doing and be patient, it will come". Is that the right train of thought? Does she need to eat more/less?

Semi-side thought....

Regarding food choices. How do you guys feel about stuff like "zero calorie spray butter"? No calories, but there are a bunch of ingredients listed. She has picked up that stuff relatively recently for flavor on veggies. I tell her that I personally don't like the stuff because it has too many ingredients and it is probably crappy for you. I think you are better off just dealing with the actual calories that are in actual butter made from milk. She then shows me the back of the bottle and says "zero calories". I choose not to fight it given the strategy of "watch calories" alone. Could this be the "source" of the plateau. That is one thing that has changed in the last month to month and a half. I struggle with it though due to correlation /= causation.