Dog growling at other dog in the home advice

[JuniperNarni]

Please can I have some advice if anyone has any.
A family member has privately rehomed a dog, shes quite old and sounds like she has been through a lot. Very loving, eager to please and well behaved. Meetings with the already resident dog went well on neutral ground.
New dog has started growling at resident dog whenever she is approached or when resident dog goes near the owners.
Is this likely to calm down? Is it an insecurity thing? Any training recommendations or does she need to be rehomed somewhere pet free?
Any knowledge and advice appreciated please.

The very best option would be to use a behaviouralist to observe and advise and to nip and issues in the bud before they arise. Do use one that only uses positive rewards based methods.

Growling is a dog's warning signal. It's a very useful indication that something is worrying a dog and it should be taken seriously. It's unwise to tell a dog off for growling or try to stop it as you have then removed it's warning signal and it's next way of telling you all is not well is a snap or a bite...

It sounds like the new Dog is unhappy with resident Dog. I'd suggest they are allowed plenty of space from each other, and are fed and walked separately.

Growling when resident Dog goes near owners is likely to be a type of resource guarding (but you really need a behaviouralist to be sure). Resource guarding over things like food, toys, bed can be addressed by making sure the dig is not given the impression he will loose these precious things so there is no need to protect them. So leave alone when eating, do not take toys off him, leave him alone when he in his bed and set things up so he knows it's his bed and it won't be removed. Resource guarding of owners is more tricky.