Holly's mum I am so glad you have had a better walk today. The way you descibe Holly is how Blossom is. It's as though she has an on/off switch for indoors and out

I get upset if people assume my 2 are aggressive. Mine like Holly both have wonderful temperaments but, their barking has been their way of controlling what they found stressful - whether excited, anxious or over-stimulated (excitement still increases adrenaline so can trigger a physiological stress response), they are not actually aggressing.
The first time Blossom's reactivity started with us was at 9 months when a Collie flew across from its owner barking and growling not long after we rehomed her. She became stranger fearful when a man went to grab his dog but, leaned over Blossom. Poor thing pooped herself. Blossom would trigger the barking and then Ziggy would take over - often not having a clue what he was barking at. However, he became the horizon watcher. In hindsight, I continued to take them into situations they weren't coping with. One such place for Blossom was the local dog park. Continuing to take them there later backfired on me.
I started Grisha's BAT training months ago: Behavioural Adjustment Therapy
http://ahimsadogtraining.com/blog/bat/ This is another really good read and technique for you. For me set ups proved difficult. I was at this point still going to the local park. I would use dogs in the distance to practise approaches and then allow Blossom to indicate when to turn away. She excelled at it for a while as did Ziggy. However it proved problematic as I could not guarantee the other dog would not come over; undoing our training. Blossom started to get over excited there - running and chasing the other dogs who came over to her. As Blossom got a little older and more confidant and dogs continued to ignore her barks, she started to charge forward and bark. Sometimes excitement driven, sometimes anxiety and sometimes hard to tell. If an approaching dog ignored her distancing behaviours and came up anyway, she was never anything but friendly. However, each time it happened, she got worse. She was also learning not to engage so much with me - I was no longer the most exciting thing. We stopped going there months ago, despite it being almost on my doorstep.
The watch me didn't prove the best for mine so, I then changed tactics again when I bought "Control Unleashed." I went with the advice of management - avoiding anything stimulating for my dogs to reduce their overall stress levels - whether from excitement (Blossom) or anxiousness (Ziggy). After a good read, I then started LAT (look at that) with both dogs individually. The good thing about LAT is that it promotes confidence in the anxious dog but, teaches focus and impulse control in an excitable dog too. It is working brilliantly for us. Progress is really being made now. I have found it useful dropping treats on the floor. Sniffing the floor is a calming behaviour and the treats rewarding. It also gives a calming signal to any approaching dogs. (Do be careful if your dog resource guards and a dog is getting closer and there are still treats on the floor. It's not a problem I've experienced but I can see the potential as I use high value treats just for LAT to increase its effect). Control Unleashed teaches much more than LAT - it has loads of advice and exercises in it.
Something I have found useful with Blossom (as she too becomes excitable once outside) is to only make progress to a walk if calm before the walk. Ie. calm behaviour - lead on. Calm behaviour walk to front door. Calm behaviour open door. Calm behaviour walk outside. Calm behaviour walk forward - there's a trend going on

Moving to the next level to get outside becomes the treat/reinforcer for the calm behaviour. The first time I ever tried to do this, it took me an hour to open the front door. Now, it takes less than 2 minutes. When I get the lead mine go and lie in there beds

Premack principle's I believe - a dog will perform an undesirable behaviour (be calm) to engage in a desirable behaviour (go for a walk). I'll get off of dog psychology now before I get out my depth as I'm not a trainer/behaviourist - I would hate to advise you wrong
Your post is really helpful to me Laura and I'm sure it will be for Holly's owner too.
A book I really like is How To handle Living With Your Dog by Winkie Spiers. It's not a training book but is exactly what it says, full of clear and easy to understand explanations and advice about how to live with your dog. It's taught me a huge amount about reading my dog's body language and the stress that us humans can inadvertantly put our dogs under.
Off to Amazon now to look at the books you've recommended and do some shopping. Thanks 
Elaine - Looks like you are going to cost me money too

I will check that book recommendation thank you

I am always open to new reads, especially dog ones.
Likewise, sharing your experiences are also very useful to me. I've read quite a few of your replies on the forum over the last few months. They've helped me no end too. This is the first time though I've been brave enough to offer any advice to others. I'm certainly learning a lot from our little furry teachers

even patience

and there is no such thing as a quick fix

I'm so sorry, this was going to be a quick reply