The answer to your question really comes down to her examination and your goals. It is possible for a cruciate ligament to be partially torn or fully torn. If it is fully torn, the knee is unstable and surgery is the best option to stabilize the knee and slow down the development of arthritis in the joint. If the cruciate ligament is only partially torn, you can see signs like you have in Hambro where she seems pretty normal unless she injures the cruciate ligament again with high activity. For a large dog who is young, partial cruciate ligament injures are often problematic because they inhibit dogs from being able to play normally without being painful, but it sounds like Hambro has done well for 6 months. Another consideration is that if she has a partial tear, she may completely tear the cruciate ligament in the future which will necessitate surgery. There is also a potential complication of cruciate injuries that involve a tear in the meniscus. If that happens, she will be consistently lame and will need surgery. Unfortunately, only you can decide on the right answer for Hambro. Surgery provides the best possibility for return to normal activity without lameness, but certainly isn't without potential risks and complications. I have attached a handout on cruciate ligament injuries below.
https://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=1975Finally, if this is a partial cruciate injury and you would like to avoid surgery, I would recommend trying to find a rehabilitation veterinarian to help you with physical therapy exercises to strengthen Hambro. They will also be able to give you a second opinion. Hopefully you can find a vet in the UK at this site.
http://www.caninerehabinstitute.com/Find_A_Therapist.htmlhttp://www.caninerehabinstitute.com/action.lassoGood luck! I hope that was helpful. Thanks for using PetCoach.