Quoting Amelia Margaret:" Will you get her fixed after she has this litter? Females are more expensive but you can usually get it done for very low cost through the Humane Society."
If you can catch them before they run out again lol. My mom had this one cat who she tried to get fixed 3 times, and everytime the damn cat would find a way out and get pregnant before her vet appointment. Mostly me and my brother wouldnt be paying attention when we came in or out, and she would make a break for it. Finally she got the cat fixed, but I just remember her being so frusterated about it lol. Female cats in heat can be sneaky, which is exactly why I have a male lol.