Calculating calorie levels for weight loss

I'm confused so of course I'm turning to Reddit. I'm working on losing weight and getting fit, and as part of that I'm working with a personal trainer. She also coaches me on my diet, and while I've loved working with her so far and I feel like she usually gives great advice, she said something tonight that just confused me. I had one day last week where I ate ~2,050 calories. She said she wasn't happy about this because it's "over maintenance." Now, I'm familiar with those online TDEE calculators so I punched in my stats to one of those and it spit out 2,500 as my maintenance level. My trainer wants me to be eating 1,500 cals per day, "and maybe an extra 100-200 snack if you really need it on a bad day." So what gives? Why does she think my maintenance calories are so low? I know the scale she has me weigh in on also gives body composition percentages - could those wildly change my calorie needs one way or the other? Of course I can ask her about this the next time I see her, I just wanted to see if there was more info out there before we have that conversation.