70% is a totally unacceptable precentage for letting a dog off leash. This is one of those areas where the dog must respond without a doubt 100% of the time or it shouldn't be happening. Earlier is better applies when they are very young puppies! IE take an 8 - 10 wk old out with you and if you have another well trained off leash dog, great. The puppy will come back and be more inclined to follow you around. By 5 or 6 months they are getting more independent, more exploring and some might say a little more deaf.
You need to either install a fence, or put your coat and shoes on and get out there with your dog if you want to continue to HAVE a dog. Do you realize how far away a dog can get in 7-8 minutes?? That's going to progress to 10 - 15 minutes, and so on. You need to train off leash in a large secure area. Somewhere that perhaps your dog doesn't realize there's a complete fence (look for public school playgrounds).
Regarding the dog not coming 100% of the time - this is a training and bonding issue. You need to be your dogs best friend for a little while. Carry small treats around in your pockets at home, and randomly call the dog. As soon as the dog comes to you give tons of praise and several good quality treats (ones the dog REALLY likes). Before long your dog will be flying to you when you say "come!" Also, you do not want to ever use the command when you can't or aren't willing to enforce it. If the dog blows you off, you need to get out there and go retreive the dog. Don't punish her for not coming, just make it clear that when she doesn't come, you'll be coming for her. Use a drag line if you need to if she's darting away from you.
If you can't afford a fence and won't go outside for potty breaks (who cares what the weather is? You don't have a fence, you make sacrifices) then at least get a strong tie-out for SUPERVISED (from inside I guess) potty breaks. Don't leave your dog out on this, ever. Just potty breaks. At least she'll be contained in your yard.
Your neighbors don't want her in their yard. Trust me. Doesn't matter if they say they "don't mind." They do. They're just being polite (which is what you should be as well, which means keeping your pets contained on your property). They didn't adopt your dog, you did. Keep her in your yard.