I'm guessing the above may be the problem...but it probably isn't for the reason others are thinking.
Weight loss is not that hard, if you are doing things correctly, it just takes time - and I commend your GF for already losing a significant amount of weight! If she taking in ~1500 calories per day and exercising regularly, she should be losing a steady ~1-2 lbs per week, assuming your BMR calculations are in the ballpark.
My guess is she is either eating way too little or too much. I tend to err on the side of it being too much, but it is hard to say without knowing your GF's eating habits. Now, back to the quoted post above. Does she actually measure her food? I often find when people eyeball measurements, they are way off. Either by too little (they think a TBSP is as much as a tsp actually is), or too much (they are using 2-3 TBSP worth when they think they are only using 1). If she is regularly consuming calorically dense food like cheese, butter, peanut butter, oil, nuts, and avocados, she may be eating 100s more calories per day than she thinks she is, which can drastically affect her perception of how much weight she is losing vs. how much she is eating. Conversely, if fat is her main source of calories (since she isn't eating meat), if she is under-measuring her fats, she may be consuming much less calories than she thinks she is.
Also, weigh only once per week at the same time each day (I prefer first thing in the morning). Daily weight fluctuations and water retention can destroy a person's weight loss confidence unless they are mentally resilient to seeing the scale swing back and forth. Back when I lost 60 lbs, my weight loss could be +/- 1.5 lbs day-to-day based on what I ate and what type of workout I did the day before, but over time, there was a consistent downward trendline.
Also, I can only say good things about reintroducing meat into her diet, but she certainly does not need to do that. For the majority situations where people are trying to lose weight, a rather wide range of macronutrient ratios will work. I've seen people lose bad weight (fat) on 10% carbs and 60% carbs. Just keep her calories focused around clean, wholesome foods, make sure she is getting adequate protein since she is not eating meat, and she should be fine.