Hey, I am having an awful time teaching our 5month lab X Zach recall. In fact earlier coming back from the park I was nearly in tears on the phone to OH because it gets so bloody frustrating. We are keeping him on the long lead because he is miles behind Daisy in the learning pathway and literally wont come back once he spots a new friend to play with.
Saying "Zach.... come!!!" really playfully just never grabs his attention so I normally have to reel him in with the long lead (which usually by this point is wrapped around his leg and the other dog, ugh). My partner says I need to be more firm and shout it like an order rather than a request so I too may try the "Zach COME HERE!" thing.
It seems that Daisy is still in the typical lab teenager stage where she is ultra confident and, like you say, weighs up the options... treat from you or fun with another dog... and then runs off to play, choosing to ignore you. I'm not sure if you've tried this and dont think im patronising you by making suggestions (lol believe me if you could've seen me down the park, I know I'm no expert)... but a dog trainer pointed out the other week that humans are soooo boring to the dog, just standing there saying "Daisy come!" with a bit of cheese as in incentive. I mean, if you were a dog wouldnt
you choose a fun playmate over a dull human? So, I think we have to make a game of it. What I've done is bought a squeaky tennis ball (easy to put in pocket). Everytime Zach sees another dog and the ears go up, I run like a looney away from him squeaking the toy. Then, I am not only offering him praise and treats, but also an equally fun game as what he would have with the other dog.
Yes it may be frustrating and Yes it will be embarrassing but hopefully soon she will learn that you are just as much fun on walk as other dogs can be
Good luck
ps. I'm so worried after reading your post thinking that I may have another year of this.... doh!!