Ahh,Cologne it's best for her and you.The last thing you need is a pregnant cat with the potential of producing up to 6 kittens etc.It also helps them live longer.Well it does in doe rabbits.Their lifespan nearly doubles if you get them spayed.Un spayed does often get uterine,mammy tumours etc.
Also cat re-homing centres are full of unwanted cats and kittens.