Once the dog is off running/chasing something there's no point in recalling them because they're not going to respond, all their focus is on the object of the chase and they literally don't hear you. You are also devaluing the recall command because they're ignoring you. Only recall your dog if you are absolutely certain that they are going to obey you, otherwise they're learning that it's ok to come back on the 5th, 6th, 7th recall - or when they feel like it/not at all. Chasing is an intrinsically rewarding behaviour - you don't have to teach the dog to like it, the chase itself is sufficient reward to keep the dog wanting to do it. At the moment, for your dog the internal thrill and reward of the chase is far, far greater than any external reinforcer you have - tennis ball, chicken etc.
This means that once chasing behaviour has become established it is very difficult to break simply because the dog enjoys doing it, and it's very hard to compete with that enjoyment - it's like you finding your absolute favourite hobby then somebody tries to stop you doing it, usually when you're right in the middle of it. It's not impossible, but it takes a huge amount of persistence and repetition because you need to reprogramme the dog to channel their chase instinct into something that you can control. You can't get rid of the chase instinct, it's hardwired into them, but you can manage and control it. This takes total persistence and consistency as every time they manage to get away and chase that internal reward system kicks in again, the behaviour is reinforced, and you put yourself back to square one. To stop them chasing things you must prevent them from doing it, absolutely and at all times. They must NEVER get the opportunity to perform the behaviour because all it does is reinforce the positive feedback loop in their brain and make it more addictive and more likely that they'll keep doing it.
Regardless of what method you use you must ensure that you maintain total control of it until your control of the dog's behaviour is proofed to a sufficient level; so if you're working them on a long line then you need to keep them on that line and control the environment they are in until you are certain that the desired alternative behaviour has been instilled and proofed in all circumstances with increasing levels of distractions up to whatever the 'ultimate' is for your dog (birds, rabbits etc.). There's no real saying how long this might take, it really depends on the individual dog and how ingrained the chase behaviour is etc. In this case you haven't given your dog nearly enough time or work yet to get to this stage, hence her taking off this morning.
There's no point in saying '(s)he has been on a line for a couple of hours/days/weeks now and hasn't chased anything, so I'll let him/her off the line in this field' because in this case the dog is only not chasing because they haven't had the opportunity to - as soon as a rabbit runs out in front of them or a bird takes off 10 feet away then bam, off they go. If the reprogramming hasn't yet happened and your control of them isn't proofed to a sufficient level and the dog is exposed to their chase triggers then they will chase - why wouldn't they? - they haven't yet learned that you're offering them anything better than the internal thrill they get from the chase.
I've been to a predatory chasing seminar with David Ryan, who is a clinical animal behaviourist and was chair of the APBC for several years. He runs these seminars regularly and they are extremely good. He also has a book called 'Stop: How to control predatory chasing in dogs' which I would recommend anyone having these issues with their dog should read. There is a lot of information on his website too, particularly this article:
http://www.dog-secrets.co.uk/how-do-i-stop-my-dog-chasing/