About integrating Gruagachan's Flexible formulaic Magic (FFM), the book's page 78 lists rules for this. It takes 30 Breakthrough points.
Ok, but what would apporpriate Insight Sources be? Supposing one finds a practitcioner of this magic, he could try and teach it, right? What about merely observing a practicioner? Perhaps using Intellego Vim to get th details of the spells?
And once integrated one is allowed to take Flexible Magic as a Mastery, but may not vary spels by more than Mastery level. Since spell parameters change in steps of 5 levels this really only is useful for spells of Mastery 5. It seems unlikely to have Mastery 10.
Especially when the two next elements which can be integrated is read. First of these allows FFM to be taught as an Ability like Parma Magica. So, how does this work? What level of ability do you need? I can guess, but if this means all Formulaic Spells can be changed by no more than ability level you need a whopping 5 before it does anything?
And the second of these extra elements mean you can change by up to 10 levels, so this sort of answers if mastery 10 is any better than just 5 for the first thing.
You need Texts, Relics, or Teachers for an insight. The rules on each are pretty well spelled out. Any Hedgie with a score in the Hedge Theory ability can serve as a teacher. The rules seem to say they need to instruct the magus for a whole season. So I would say just observing power being used is not enough. No matter how much magic one uses.
I'd be fine with a season worth of observation counting as a Season of the hedge wizard acting as a "teacher". For example, if the magus can manage to set himself up so that he can scry on the hedge wizard for the whole season that would count as an Insight Source. Of course, the hedge wizard would need to actually be using his magic during that season (i.e. probably doing his own seasonal supernatural long-term activities).
Just observing the hedge magic briefly cast (say, you are out Adventuring and the hedge wizard casts spells at you) probably wouldn't count.
Just the practice of magic doesn't provide an insight though; the practitioner need some understanding of how the magic works. The rules require a "Teacher" to actually have the relevant hedge magic theory to provide an insight. To me that means there must be some sort of discourse for a Hedgie to be able to provide real insight. It could be forced or magically induced but you need access to the understanding of the magic not the ability to create an effect.
This might give the Magus exposure or practice points towards the relevant theory ability(in this case the Pictish language). Once the Magus has a score in the ability they could provide their own insight.
I think it is really that the observer needs to get some understanding of how the magic works. Which is certainly easier if you can discourse in an intelligent manner with the Hedge wizard. But I don't think it should be impossible to gain "similar" knowledge by extended observation.
A "laboratory" is actually given in HMRE as an example of a "relic" that can be studied for Insight. So, I think it is fine for a magus who is not physically present in the "laboratory" but is making observations (via scrying, or some other method) of the functioning "laboratory" using those observations as a source of insight. So, perhaps rather than "teacher" the observations of a functioning laboratory should strictly count as a "relic"; either way, it seems a plausible source of Insight.
Also, remember that when you study an Insight source you need to make a Int + Magic Theory roll against an Ease Factor of 18 to actually gain the Insight. If the source is a bit substandard, then you can always add a penalty to this roll to represent that.
If she is a "teacher", using the teaching rules in HMRE, yes, she needs a Hedge Magic Theory score to provide insight.
However, if the hedge wizard doesn't have a Hedge Magic Score (or even if she does) she can still produce artifacts/"relics" which can be studied for Insight. A "Laboratory" is explicitly listed as a "relic" that can be studied in this way.
The HMRE rules appear to have anticipated that the magus would be in physical possession of the laboratory --- i.e. he has disposed of the hedge wizard and captured her lab. However, scrying on a functioning laboratory for a season sounds like an entirely plausible, alternative way of using a laboratory for a source of Insight. It's not as good as "teaching"; because a teacher adds a bonus to the Insight roll, which merely observing the functioning laboratory will not get, and a laboratory only provides one Insight, whereas a teacher can provide multiple Insights.
IMS gaining an insight is a lab activity that benefits from applicable laboratory bonuses and generates a text. So relics even other labs need to be analyzed in a laboratory just like any other magic item. For that matter I require a researcher to analyze Texts or gain an insight from a Teacher in a lab also. I admit it may not be RAW although I wouldn't be surprised if that's the way RAW is supposed to work.
Admittedly the logistics of a lab within a lab are head scratchy, but with a little imagination and stretching the rules in Covenants can account for it. (I had a Learned Magician who was a member of the Order. He set up a Hermetic and Hedge Lab adjacent to each other in the same "space")
Also if Hedgies follow the same rules as Hermetics you do need a MT ability to set up a "Lab"