adding a new JRT

Question
We have a 13 year old JRT female. Still acts like a puppy but sleeping a lot more and gas cognitive heart disease, so not that long to go. Had her since she was a puppy. We will definitely get another JRT. Know the breed well. We have the opportunity to adopt a friends 1 year old male JRT. Its a great opportunity but I don't want to stress our old baby in her last year(s). We will do an introduction this weekend. Our female is very socialized and loves other dogs. We made the mistake of adding another female JRT puppy when she was 8. Her mother instincts really kicked in and all was great until the other female was about 1. Then the jealously kicked in for both. Fine when they were together but vied for our attention as the number 1 dog. We found a great home for the other female (we loved her but) and she's doing great 5 hers later. Home that had an unsocialized 8 year old male, who, after a few fights, allowed himself to be dominated and they live happily.
So, given the jealousy history, but, also given that this is a 1 year old male with both dogs having a nice personality, should we consider this? We know we need to make sure our old friend feels just as important as ever. We lido need to assimilate a new family member so can't ignore him. Both dogs are elective fence trained and we have a doggy door. Our female has full in/out fun privilege. The 1 year old male we are considering has not had doggy door freedom but is fence trained. Is that a potential issue. Thank you for you advice.

Answer
Hi Andre,

I wish I had an easy answer for you -  
As you know, Jacks can be fickle and funny; There's just no way to know if they are a good match for each other. It's great that you are having an introduction this weekend, so see how it goes.  I'm sure at her age, your female will love everyone and anyone. Are you able to bring the male in for a "trial" period? Is the male neutered? Neutered will be a little less dominant but remember with ALL males, they mark their territory so you'll have to be very diligent with RE-TRAINING him to go outside.  Personally, just my opinion, I would wait and give your girl all the attention she deserves until she dies. She's sick anyway and no stress is good. A male JRT is going to be a lot of work, so if you do take him, be prepared. When you do the introduction,make sure it's done outside and make sure your female leads the way in so that the male is FOLLOWING her in. This immediately establishes his place within the home.  Make sure they have their own beds, own toys, own bowls, no sharing anything at first.  This will make the female feel less like she's being replaced.  Shower female with lots of extra love and attention, which you are probably doing anyway, and make sure to spend alone time with each.
Wishing you the very best of luck with whatever you decide!!!!