Thats an interesting video J.
Luna is walking well, and most importantly she's keeping an eye on you.
Its difficult to comment too much from a video, but what comes across to me is that Luna is doing the exercise because she thinks thats what you want and not really doing it because she enjoys it, of course she should do it because you want her to, but she should also be doing it because she wants to.
I'm not quite sure how to approach this, but I think the quickest route would be to really go back to basics, this could mean only playing with Luna for a few weeks and not giving her any commands at all, this won't give you a blank canvas, but I would hope it will make it a little easier for Luna to understand what you want her to do, I'm thinking maybe there's a clash between the Obediance and the new training.
I don't know anything about obediance but I would assume that the handler does the thinking for the dog, I don't mean that to sound they way it probably does, I mean the handler gives the dog a command which the dog knows involves it doing a certain thing and the dog goes and does that thing, gundog training is slightly different in that you are using the qualities that have been bred in to the dog, ie retrieving in labradors, and quartering in spaniels which you then develop through the training, and essentially the dog knows through breeding what it needs to do, but with training you shape its behaviour to the way you want it all to happen and where you want it to happen. As we can see from the video, Luna is already displlaying one of those qualities as a retiever which is carrying an item in her mouth, the trick now is to shape that in to carrying anything you ask her to do, the dummy in this case.
What you really need to do in the first instance is to get Luna focused on retrieving, tennisballs or what ever, the way to do this is as AMTS has already said, to make it a fantastic game with you being as silly as you can, get down to Luna's level, no commands, just play, do it indoors if your not comfortable with being seen doing it, teasing Luna with a toy, not quite letting her get it is a good way of getting her wanting something, then let her have it and you try to get it off her with out quite managing to get it off her.
Once you've got Luna wanting an item then you can start wrestling it off her playfully and throwing it away, she'll start chasing after it and bringing it back to you to carry on the game, then the training can really start.
I'm not going to say what the next stage is, I think its important we get Luna playing with you, and you happy with playing with Luna.
It might be that what I've said is irrelevant or not applicable, if so ignore me and I'll go back to my corner
As a postnote I would be a little concerned that you are actually trying too hard with the retrieves and giving her too many, so she could become bored with it, I'm actually training a 10 month old springer at the moment and brushing up on the training of a 3 year old who's gone a little rusty, my fault as AMTS has already pointed out to me, (something about no bad dogs just bad handlers
point taken
)
To give you an idea of of the way I train retrieves with the 10 month old springer, I have a peg which I push in to the ground, I put the dog on the slip lead with the lead attached to the peg, I then stand on the lead so there is a little pressure, the lead is barely taut, I then throw the dummy talking to the dog all the time and reminding her what a good girl she is sitting there, I then steady her for a second or two before walking out and getting the dummy my self, get back to her put the dummy away out of sight and give her loads of fuss and kisses cos' she's so clever sitting and waiting for me to come back.
I do this may be 6 or 7 times then 3rd or 4th time I slip the lead of so she hardly knows I've done it, give her loads of fuss talking to all the time again, then I say "find it" and off she goes like lightening for the retrieve and straight back to me
but I only ever let her retreive once maybe twice if the first was a good retrieve.
As you can see the dog doesn't do much retrieving, the idea is to make the dog hungry for the retrieve, and loose a bit of weight my self with all that retrieving
give them to many retrieves and they get full up on it and can't be bothered.
When I walk the older springer we'll be out for an hour or two and I'll give her a blind retreive over a hedge in to a field and then I'll drop the dummy in the long grass a couple of times walk on and send her back, and thats it.
Probably a load of nonsense, but maybe it will help in some small way.