I agree expectations around essential calories is rarely realistic. And as others have said, if your metabolism has been messed up historically, your body will be extremely efficient at storing calories not burning them.
As others have said, while you're still on the jabs, now is the time to do the other half of what they suggest in conjunction - get better habits in place ready to wean down the dose.
'Lift heavy' is ubiquitous already. In practice, it means 3 months getting used to a regular session focused on muscle strengthening rather than heavy cardio 2 or 3 times a week. For most women who haven't ever weight trained, a circuits class, women who lift, or simple dumbbell & body weight routine at home can be enough to stimulate muscle growth-especially after weight loss.
Get at least a couple of sessions with a trainer who works with women. If they don't mention strengthening your pelvic floor within the first 15 minutes, there's a risk you can overload the other exercises & not have the strength you'll want in 10 & 20 years time to support your organs! So find someone who can assess how you use your posture & set up for exercises before you add any load.
If you don't fancy doing anything at a public gym, https://mamamadestrong.com is a fabulous follow along program to assess your own strengths & weaknesses & help balance and strengthen core before moving to lifting heavier weights in general.
Once you've figured out how 3 months worth of consistently doing at least 2 strength led sessions around the exercise you already enjoy, your tendons, joints & bones will have adapted (and you probably will have toned up a bit with more muscle mass already). Then it's a question of focusing on picking about 4-8 strength exercises & doing them consistently for another 8 weeks before you change your routine much. Either lower body/upper body split, or a selection that covers both. Ideally you should do each muscle group at least twice a week, because muscle only grows once it's been used to its breakdown point (and you feed it enough protein & rest afterwards).
An efficient home dumbell routine might be
1 goblet squats into calf raises
2 single leg deadlifts with one foot pushing against a wall behind you and weight in opposite hand from leg you stand on, then a shoulder press up each rep
3 backward lunge, then side raise & forward punch with your arms after you've lunged each leg
4 a row then a bicep curl
ideally with the weight high enough that you can do 5-8 well, but not many more. It doesn't hurt at all to start lighter and get to 12 or 15 before you feel you're going to cheat the move or have bad posture to keep going though - that's why working with a trainer for a couple of sessions can spare a lot of injuries, but don't stop while it's really easy.
The aim would be to do 3 rounds of however many reps you can get to on each of the 4 exercises. It might be 8 reps on the first round and only 4 on the 3rd round, that's ok. Good form is more important than number of reps.
Dead serious trainers would say wait 3 minutes between each. But being time efficient is a thing too, so moving through all 4 then having a 2-3 min rest & shake out would be fine too!
If you get bored easily, pick 2 or 3 "finishers" to add at the end. Swap these as much as you like to hit little muscles - sit ups, parachute jump lifts (face down on floor & lift legs & arms), tricep dips on a chair or bench, planks, step ups, boxing with a dumbell, star jumps, burpees (??? would anyone do those by choice?!) just 30-60 seconds hard of as many as you can do, a couple of times for 2 or 3 of them.
Then stretch out, eat something with protein and carb in it within 30 minutes, sleep lots that night & make sure you get a decent breakfast & lunch with at least 30g of protein in each the next day.
If a weight gets easy, add a couple of reps to keep the last ones hard with good form. Once you can do 8-10 well in all 3 rounds, choose a slightly higher weight the next session.
Doing the session above twice a week would cover all your major muscle groups and keep a bit of variety at the end.
After a 3 months easing in and 2 months of that circuit, you will unavoidably have a much stronger body than now.
Which would burn more calories at rest and you'd probably find easing your dose down will be more manageable.
Don't try to mix up losing weight with a sustained period of heavy lifting though. You need enough calories to build muscle! Maybe starting the 3 month getting used to it weight sessions while you continue to drop steadily would be a good idea? Don't be scared to "only" lose 2 lb a month at this stage though, and add a snack (15-20g of both protein and carb) within 30 minutes of finishing a weights session to refuel so your muscles can mend.
Once you've got through the 3 months of easing your body into it, you don't really want to be in calorie deficit if you're lifting weights with progressive overload every week. Your body needs to mend & lots of veggies, fibre and a sensible amount of protein (100g a day for your size) will be needed to keep going without getting exhausted or injured! And don't skimp on sleep or water.
6 months from now, you'd probably find your resting metabolic rate is somewhere more like 1300-400 calories a day.
It is possible to train a body back out of slow metabolism, but unlike losing body fat, there aren't really any shortcuts. You've had the help to get to a size you're much happier with, invest the time in that to make it stronger and more energy-burning for the long term!
And eat enough fibre. It helps with fullness, digestion, and damping down the cravings for the high-energy junky stuff that makes it far too easy to over consume. Don't tell yourself there's any demon foods, but just manage them as proper rare (once a fortnight, once a month) type treats.
There is no bad week. If you have a blowout meal or miss a session, don't write off the whole week, just pick up & keep going.
You've got this. And you'll be ready for when things slow down further in your 40s if you invest the time now!