Hi,
It's a hard one but my advice would be to go back to basics.
How is she motivated? Toys or treats or both?

I don't know a huge amount about springers but I own a collie myself and in my experience, they tend to work on rails so to speak, especially the worky ones.
I find my collie's love of toys (in particular ball) really useful in recall training and all forms of training. But he's one of those who loves his toys but won't say no to a nice treat if it is up for grabs too.

Perhaps take the training back on to a longline in the fields where she looses her concentration. Also you said she enjoys playing ball but looses concentration as she gets bored, I'd say stop the game of ball before she gets bored if that is possible.
If you can get a friend or family member to join you, play some recall games. Each have some really tasty treats and call her inbetween you treat and praising her lots and lots when she comes. You may sound like a wally praising her madly but it is worth it as the positive associations made between her coming to you and the praise and treats will reinforce her recall.
Another point is try and make yourself really interesting. More interesting then anything she might wonder off to explore. If you have a friend with you, hide and seek games and randomly running away from her (but keeping her in your eyesight) could be good (keep her on a long line if need be at first then proggress to offlead). You could even give these games a try indoors too. This makes you unpredictable and so you will find her keeping a closer eye on where you are.

You may find this article really useful:
Why won't my dog come back? | Behaviour & Training

Hope this helps

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