First an foremost you need to find out if there is a leash/containment law for cats in your area. Usually only cities have these laws, so if you are like me and live in a rural area you are SOL. I understand how you feel. I am a huge animal lover (in fact I'm vegan) but one house in our neighborhood is responsible for the feral cat population that live amongst us. I too have been woken up at 2am by cats yowling on my deck, and smelled the fresh tom cat urine first thing in the morning. It is gross. My husband and I picked up everything around the outside of our property that may seem "inviting" to cats. We have ducks, and chickens so a wheelbarrow full of hay is the perfect bed! If you aren't familiar with cats it may be hard to identify what might be attracting them to your property. Look for puddles of water, shelter from the elements, cozy napping areas, etc. If she is hanging out there now, chances are she may try to have her babies there too. The main problem here is that these cats are not spayed, and neutered. Most areas now days have programs to fund the spay/neuter of less fortunate animals. It isn't your responsibility since it isn't your cat, but the issue does need to be addressed. I wish you the best of luck. What my husband and I have done has worked for 2 years now, hopefully you will find it useful as well.