I'd say u want to go back to basics and get it right before u take it stalking again, no fun for u or dog and just teaching it bad habits.
The adapting a slip lead to a halter does work with very determined pullers, (only thing that worked for my wire and worst puller i've ever had), althou on 'normal' dogs so does either turning 180 everytime dog goes in froont or waving a stick infront of its nose as 6p mentioned, i wave the stick all the time like a pendulum so dog can see it in front and walks into it. Just keep at it and be 100% consistant, no good letting her away with it some of the time and not others. the instant she creeps 1 inch forward u have to be on her then, no good letting her creep and creep and then give her a row. If u do that she's not sure where heel is is? is it level?, 1 ft forward? or 11/2 ft ? Has to be instant so no doubt in her head
Also mind and praise her when in right place (even odd treats possibly) bt make sure it is in the exact right place or ur praising bad behaviour. Walking slower and walking in zig zags (or constantly change speed and direction) basically so dog has to concentrate harder, really go back to pupppy training
Perhaps taking her walking in woods more often (albeit without rifle) might densenitise her to ur stalking gear so she's less excited (althou the rifle will probably then become the trigger)
Does the dog walk well on a normal lead but not on ur stalking/jeagger lead? Perhaps dog has learned it won't get told off or direction changed when in stalking mode so can take the p**s with no fear off a row (as ur busy stalking and don't want a noise) Also most dogs are bloody clever and know as soon as u are not concentrating 100% on them and will push things a bit to see wot they can get away with and keep pushing
Hpr's are not the easiest dogs to train to heel at times, but possibly ur timing/or commands are out and she thinks heel is something else or she may just not respect u (dominat) so is just taking the p**s.
A 1-1 lesson/help of a decent trainer or pro could probably give/show u a few tricks to sort this out pretty quickly as they can see u both and read the ody lanuage.Be well worth it as otherwise u will have the next 10 years stalking with her pulling like a train