What's the best way to introduce two female dogs when one is jealous?

I would recommend giving Maddy a very slow introduction to the new dog. You should be sure to spend time alone with Maddy at least once a day, and she should have a little time each day to have the house to herself as well. I would recommend keeping them mostly separate for a few days to weeks: they can sniff each other through a closed door at first then have short periods of time together supervised. If someone gets upset, they should be separated again. You may be surprised - Maddy might get along great right off the bat with the new dog but don't be discouraged if it takes awhile. You also might want to consider purchasing a pheromone spray like Feliway to help decrease her stress.

Consider a pheromone product, such as the Adaptil collar or DAP plug in diffuser, to help decrease any anxiety or aggression. You can also have your new partner feed, play with and walk Leia so that she gets used to her/him being around and associates "good things" with her/him.

Female to female aggression is very hard to manage. Are all your pets spayed and neutered? This is the first thing I would do if not. Some of the worst injuries I have seen are between two females in the same household. They are likely establishing dominance and there are things you can do to reinforce the “leader” by feeding them first (or feed them all separately), letting the alpha dog walk in front when taking walks. I strongly suggest you work with a behaviorist and take aggression seriously bc I have seen it escalate quickly. Hope that helps.

Separate them for a few days then gradually reintroduce them. First with a door between them so they can hear and smell one another then separated so they can see but not reach one another and finally a supervised physical introduction. Use leash, collars and muzzles if necessary. Pheromone products such as the Adaptil collar or DAP plug in diffuser may decrease any anxiety or aggression. Provide adequate numbers of bowls, beds and toys to prevent food aggression or resource protection.

Introducing a new dog into the house can certainly pose some challenges. Female/female dog pairings have a higher rate of problems than male/female dog pairings. Initially, keeping the dogs in separate rooms with a solid door between them can be beneficial. Allow them to smell one another under the door for a few days, then use an open barrier, such as a baby gate between them. This will allow them to see and smell one another without direct contact. A slow introduction can ease the transition. If both dogs are food motivated, try giving each a small treat at the same time. Avoid giving a larger treat that the dogs would need to put down to chew as this could create additional problems. Hope this helps!

It may take some time for her to accept him. If she is being aggressive toward him than you should not allow them to be together unsupervised, espeically around feeding time or any toys/bones that she may protect. Give her extra attention, praise, and treats while the puppy is around so she knows he is not there to replace her. You could also try an Adaptil collar or diffuser and see if that helps. If she doesn't start accepting him than you could talk to your vet about trying an anti-anxiety medication, like Prozac or Trazodone and see if that helps.

Any introduction should be done gradually and on "neutral" ground. You can use a pheromone product such as an Adaptil collar to decrease anxiety or aggression. Introductions should start with Max being able to hear and smell a new dog but not see him. This can be done a friend's house or perhaps a family member's home. Again, some place neutral to both dogs. Once he is acclimated, he should be able to see the new dog but have no physical contact. This can be done using the fence at a dog park. Eventually, you will be able to physically introduce Max to the dog. Use a leash on both dogs for safety and muzzles if necessary. Go slowly, don't force him but correct any negative or aggressive behaviors immediately. Praise and reward him as he progresses.