We have a 20 month old female miniature schnauzer. She was a lockdown puppy, and has been nervous of other dogs and people she doesn't know since she was very young. We have also had a some issues with resource guarding (food related) and she has snapped at my 13 year old dd a few times, in hindsight we could see the triggers and have worked with all of our children to help them be mindful of when to give her space etc. This evening she snapped really nastily at dd again. There didn't appear to be any trigger this time, she was sitting on the sofa next to dh, dd was sitting on the other side and began to stroke her. She seemed happy enough and then suddenly snapped and actually tried to bite dd (luckily missed). Dd is devastated, she was already a bit wary of the dog due to the earlier snapping issues, and now says she is scared of her. I am at a loss of what to do next. We have worked through lots of advice about nervous dogs and thought things were getting better, but were obviously wrong. I am particularly worried as my younger dd has a learning disability and - although we always closely supervise her interactions with the dog, I feel like she could inadvertently trigger a snapping/biting incident - her reactions are much slower than older dd's, so may well not move away quick enough to avoid getting bitten. I'm not sure what I'm looking for really - do we need to rehome our dog? She is very closely bonded with me and (particularly) dh, so it feels like this would be very unfair to her, but at the same time I can't see how we can make it work with this level of unpredictability.