Greetings, and thanks for the question! Apologies for the delay, I just got in for the evening and saw your post.
Firstly, to set your mind at ease, Gabby is not showing any of the common signs of pain. Based on your description of her history, what she is doing is a somewhat uncommon, but otherwise a normal behavior.
This is what she is experiencing: since she has been on probiotics since her colic episode, it's most likely that the normal flora in her gut is somewhat disrupted. If you have spent any time around young foals, it's very common for them to eat their mothers' manure. This is a normal and necessary activity, as the manure contains the microbes necessary for the production of a normal gut flora. This is needed for proper digestion. As Gabby has been on the probiotics, it may have been a bit too much and she is only getting her gut back to normal.
As far as the lifting of her upper lip, this is also a very normal behavior called the "Flehman" response, and is a way for the horse to open up it's scent ability, which is in response to certain smells. This is extremely common with the stallion during breeding season when he smells the scent of the mare's urine that is in heat. A link below shows you a little more of a detailed description.
So overall I would say that Gabby is doing very well!
Again, my apologies for the late response. I hope this has been a help to you, and please let me know if you have any further questions.
All the best to you and Gabby,