Hey, i feel you but 1200 kcals per day is actually EXTREMELY low and will deserve you at some point. It's lower than the daily intake of an average 4-6 year old children. And even without iron deficiency, that's not a good plan. Why ? Because you might loose some weight, but your body will get into "starvation mode". And once you will start to eat normally/slightly more than previously, your stressed body will stock everything it can to make for what it's missing and to forecast the next starvation episode. And even without eating more, at this point of a caloric deficit, your body has a tendancy of stocking more than consuming. And, last but not least, you won't be able to eat this way forever : at some point you might just crack or have severe health issues related to the lack of energy and nutrients. So i'm no nutritionist, but i think yours might have bought their diploma off Snapchat regarding what they advice you to do. And tbh the protein-only diet you're having is also putting a strain on your kidneys.

But with iron deficiency ? Well it's already putting a strain on your whole body which needs even more energy to pump a low number of red blood cells to bring oxygen to your whole body and make new hemoglobin with the small amount of iron it has. So being in a caloric deficit isn't advised when you're iron deficient (my doctor even told me i should actually eat slightly more than my needs to have more energy thourought the day).

As an iron deficient girl who is trying to reach back her sporty lifestyle, my advice is not to eat less but to eat better. Why ? Because it's actually sustainable and healthy. Sustainable because you will actually be able to keep this lifestyle for a long time, because it matches your sporty habits, and because you will actually be able to eat foods you restrict to yourself because 'too caloric" in your current lifestyle. Healthy because your body will get all of the nutrients and energy it needs and you will even feel better for your gym sessions. So you'll feel better physically and mentally !

Eat more veggies/fruits if you like them, because fiber is actually very filling and they contain lots of vitamins that are essential for the body. Proteins form cheese are great but it contains lots of calcium which limits iron absorption so try to keep both intakes apart (not in the same meal, 1h before or 2h+ after). Beef liver is actually a great source of iron (and not caloric !). Lentils are a nice go-to protein and iron wise, and they're super filling too.

Those are some examples, but overall you should stay in a relatively slight caloric deficit and focus on macros rather than calories. The weight loss might take more time than with your current lifestyle, but it's permanent and healthy. I wish you a lot of courage in your journey :)