First of all, it is common for female cats that are related or good friends to co-rear a litter of kittens. However, they usually both have kittens at the same time.
There is something called a psuedopregnancy, where cats produce milk without kittens.
Is it possible that Tyger had kittens longer than six months ago and is now helping to nurse the new litter?
As you don't know for sure and as there may be kittens that are relying solely on Tyger for milk, I think it would be best if you released her ASAP. There is very little chance of the kittens ripping open her stitches. I've spayed feral mothers when the kittens were around 8 weeks old. They went back to caring for the litter and the spay healed up without any problems.
Just keep an eye on her. If she seems unwell or you notice any bleeding you may need to trap her again.
There is something called a psuedopregnancy, where cats produce milk without kittens.
Is it possible that Tyger had kittens longer than six months ago and is now helping to nurse the new litter?
As you don't know for sure and as there may be kittens that are relying solely on Tyger for milk, I think it would be best if you released her ASAP. There is very little chance of the kittens ripping open her stitches. I've spayed feral mothers when the kittens were around 8 weeks old. They went back to caring for the litter and the spay healed up without any problems.
Just keep an eye on her. If she seems unwell or you notice any bleeding you may need to trap her again.