Good for you Marko!
Fostering is so rewarding and of course comes with the gift/risk of "failing"
I'm a "Foster Failure"
and am very happy to be part of that club
As for introducing a new kitty, it depends on the personality of Twiggy. If she is dominant I would introduce them very carefully. Both should be confined in crates and placed within sight of each other for 10-15 minutes. If all goes well you can move them closer and closer until you are then able to release the most calm kitty. How they each react would dictate how quickly you can then progress. If either or both get aggressive they will need lots of time apart in their separate areas with regular and repeat introductions. Placing a blanket from Twiggy into the foster kitty's area and vice versa is also a good idea so they can smell each other in safety.
I'm a bit excessive when it comes to safety as a cat fight would be horrific to witness and almost impossible to breakup before an injury.
Looking forward to hearing all about your Foster kitty
