TDEE takes cardio into account. if she burns 1300kcals doing cardio (on average per day) her TDEE MUST be higher than 1300cals.
dont think about going to the gym and going on the bike until is says 500cals, and think "today i am 500cals less fat", when you calculate your tdee this will be account for. If her TDEE is 1300kcal and she wants to lose 1300kcal of mass per day, she must eat nothing.

TDEE is calculate by BMR(basal metabolic rate; what your body consumes doing nothing but maintaining homeostasis) multiplied by Activity coefficient.
your TDEE is what you burn on average per day, so if you eat the caloric amount of of your TDEE you will burn exactly what you eat. You will not store food as fat or muscle, and you will not need to breakdown fat or muscle for energy, thus you will stay the same weight and probably the same bf% unless you doing it long enough to convert fat to muscle.

my TDEE is about 3300 (BMR~1900x1.7(this is where i rate my activity level, because of how much I train, how much cardio I do and general activity) i eat 3600cals a day, therefore i have an extra 300cals everyday added to my body, because im dieting properly and taking measures to combat fat gain this is almost entirely turned to muscle.

The limit under TDEE that burns LBM, this is dependant upon many factors, such as macro split, food quality, your bodies physical condition, and training schedule. I would not go below 20% unless you are on hormones, probably start with 10-15% and see how you do.

1kg of fat (just pure fat) is 9000kcal, but body fat contains water and isnt pure lipid, I bet around 8000kcal.