I think every body has said this, but do you REALLY want to contribute to a dog over population and high kill rates in shelter? It may seem to you that there is no connection, but let me assure you there is very much one. Just read this:
http://www.almosthomerescue.org/whatisbyb/whatisbyb.htm
http://www.usatoday.com/life/lifestyle/pets/2010-07-08-vetviews08_N.htm
http://www.jlhweb.net/Boxermap/reputablebreeder.html
If you truly love animals, you'll look out for their welfare than you desire/quest of satisfaction of birthing puppies.
Also, do you know if these puppies will have a permanent home where the owners won't want to get rid of them if they move, get divorced, have kids, etc over the 10-15 years of the dog's life time?
Do you know if your dog and your neighbour's dog are free of any genetic faults? Because many genetic faults never show up in the dog but are passed on (arthritis, poor vision, bad hips, etc).
Besides, a 6 year old female is at the end of her fertility--which means there is a very, very high risk of her having major pregnancy complications which could result in defective puppies, miscarriage or even death of both mother and/or babies.
Add to this a Jack Russell is significantly larger than a Chi, a breed that already is small framed and that has a difficult time staying pregnant and birthing.
Please do yourself, your dog and everyone a favour. Don't breed your dog that you love so much!
參考: Owner of 6 dogs, actively do dog rescue of abandoned dogs in pounds and streets.