it's that time of year when kitties are in the mood for lovin' - and the tom has followed yur kitty or her scent to your back door. i had a ginger tom sat in my garden doing the same a few days ago.....he had the misfortune of having all 3 of my ladies going out at 8am (while he was sat there), who promptly beat him to a pulp! you can keep yours in for a few days if you want - she will be no worse off for it, or let her out to sort her own battles out, either is fine....she will encounter other cats anyway. much will depend on the character of your cat - if she is timid i would keep her in, or if she is desperate to go out i would let her out. good luck with whatever you decide x