terrier getting more aggressive

[Eve]

despite being very well socialised, exercised etc our jack russell has always been very protective and not social (read attack 1st make friends later ) towards other dogs or people.

She is walked regularly ( on lead and with a muzzle on), is not left on her own for long periods etc etc

She has always been very cuddly with my children and never aggressive to them , but unfortunately has now bitten and gone for some people who have come into our house regularly.

Not something I want to continue obviously.. any suggestions? Would a dog behaviour expert assist?

What were the circumstances leading up to bite?

Contacting an APBC registered behaviourist would be a very good starting point. Then a good look at how to manage the situation in the meantime so no one is hurt and she doesn't rehearse the behaviour.

Oh eve, I'm sorry that sounds distressing for you.
Are you sure she's not frightened? Mine a bit of a scardey cat and barks to warn people away, rather than being protective. She hadn't ever gotten but I think she might if pushed so it's something I have to keep an eye on.
I would definitely keep him desperate if you have other children visiting, just don't risk it.

Get a behavioural expert in, yes.

God I hate this kindle
Gotten should say bitten
Desperate should say separate