Calorie burn accurate?

Once the Garmin adjustment kicks in, it's pretty much Garmin running the show, not MFP.

Yes, heavier people burn more calories (in general) than thinner people of the same height, doing the same thing: You are moving more pounds through the world, every single minute.

Further, the calorie adjustment (between MFP and Garmin) will be bigger or smaller depending on how your "activity level" in MFP is set. Did you say you are sedentary? A lot of women with families are at least lightly active, taking care of the child/children and home. The adjustment (your 555 calorie number) is the estimated difference between how much MFP expected you to move in your day (total, not just exercise), and how much the tracker thinks you actually burned.

For most people - average people - the trackers can be pretty close. For unusual people - who may be unusual for non-obvious reasons - they can be materially high or low.

The thing to do is to follow the recommendation for at least one full menstrual period (so you can compare body weight at the same relative point in at least two different cycles), then look at average weight loss per week in that time period. If you're close to your target, all is well. If you're faster or slower, adjust your intake based on actual results. Keep paying attention to that expected vs. actual, and tweaking as needed.

For me, Garmin's estimate of all-day calories is way lower than reality, as compared with 7+ years of calorie logging and weight results experience. MFP's estimate is also way lower. That's unusual, but not impossible (obviously). What I'd recommend you do is to hang in there for the "at least one menstrual cycle", and see what your results turn out to be.

Losing meaningful amounts of weight is a long game, and favors patient analysis.

Also a Garmin user here. The daily estimate for a sedentary day is not too bad for me, if probably a bit too low by about 150-200 calories. No biggie. Running is quite spot-on for me. Cycling estimates a bit too low, and hiking totally overstated. I mean, I hiked 15km today and Garmin gave me 1028 calories. Yeah, i touched upon a HR of 175 and it's hot today, thus both probably had some influence on the high number. But even walks in colder weather on totally flat terrain are ridiculous for me.