She will not go up to other dogs but will attack them if they approach her. Can you offer any advice?
First you have to identify the cause of the aggression. As she does not seek to fight other dogs as a dominant animal would do, then I suspect that her aggressive attitude is most likely caused by fear, or perhaps because she is just protecting her pack – namely you!
The correct levels of socialisation usually help avoid this type of aggression beginning and though it is always easy to see things in hindsight, it is not too late to undertake a sensible course of socialisation, just as one would a puppy. This will not be a quick fix and you may need the assistance of an experienced dog training instructor, either through referral by your veterinary practice or by contacting the Kennel Club Accreditation Scheme specialist, Sue Evans.
Her email is firstname.lastname@example.org. Alternatively, visit www.thekennelclub.org.uk for more contact details. Sue can put you in touch with a Kennel Club accredited instructor who deals with this type of problem.