If she's ignoring recall/stop when there's game present then the behaviours haven't been proofed to a high enough level, and she hasn't had enough steadiness work on live game in controlled conditions (which is basically more proofing). If a dog has perfect stop/recall then they will do it no matter what distractions are there and to get to that stage you need to gradually proof and test the behaviour in increasingly distracting environments and with increasingly 'attractive' stimuli, working your way up to pheasants, rabbits etc. which are generally the ultimate distraction for spaniels.
For now you need to go back to basics and drilling in the recall and stop with no distractions and then start gradually increasing the distraction levels. You could rush in and start taking her to a rabbit pen etc. to work on her steadiness straight away but if you go back for a while and repeat everything until she is listening to you no matter what else is going on it'll give you a much firmer foundation. It's vital you don't let her practise the chase behaviour again though, every time she does it and ignores a recall or stop you put yourself back to square one. Do not take her anywhere where she is going to find any game, and if you have to or you're not sure if there's any there then put a trailing line on her with some knots tied in it that you can stand on if she ignores the whistle - and make sure you're always in a position to stand on it if you need to! If you're training her for working she shouldn't be ranging far from you anyway, when I'm training a pup for working they go no more than about 7-10 yards from me unless we're doing a retrieve and then I make sure there are no distractions that could spring up. Never start repeating the whistle cue, if you recall or stop her and she ignores it don't stand doing it over and over - go and get her, bring her back to where she was when she ignored you and make her sit there - but better to not give her the opportunity to ignore you in the first place by ensuring that she is focussing on you while you work on her response and steadiness and that she's not ranging too far from you.
A good gundog trainer will be able to help you, and provide access to a rabbit or pheasant pen at the appropriate time so you can work on her steadiness in controlled conditions once you've proofed her recall and stop to a sufficient level, although I would steer clear of anyone who uses harsh methods.
