Do you have firm ideas about what you want her to be able to do? Any "big projects" in mind with Herbam?
Let me take a look at something and I think I have an idea to pitch to you, but in the interim I think real direction here should come from thinking about your character goals.
Do you have firm ideas about what you want her to be able to do? Any "big projects" in mind with Herbam?
No 
Her immediate goal would be to find a place into the world for herself. That would be her lab and garden. And it could include an enchanted Tree to help her in lab work (like The Tireless Servant but with Herbam). Thats would be her biggest project...
Then, it depends of what she learns from the world and the people around her. I have some ideas if nothing happens, but none of them revolves around Herbam in itself.
The first thing that came to mind was Ranulf from Magi of Hermes and his Major Focus: Unnatural Fires. You could probably convert this to Herbam as Unnatural Plants rather directly. And then reduce it to a Minor in some way if/as desired. That would allow for very "strange" plants as it were, much as Ranulf makes very unusual use of Ignem.
Or I think something else thematic might be something along the lines of "Plant Health" to cover healing, growing, or destroying plants ... but not more esoteric uses.
Thoughts?
It's very interesting.... i like a lot your idea about "Plant Health" too (but i would change the "destroying plants" concept to "pruning plants" 
). It could be called "Minor Focus: Green Thumb" xD
I love it!
Edit: Yet, the more i think about it, more it seems like a Major Focus... D:
I would define Plant Health likely as a major as well. But I'd define it as healing/harming, curing/diseasing, and growing/withering any plants.
You could take a subset of those, or also restrict the plants it applies to, to bring it down to a minor.
Like ... Tree Health, since her interest in Forests and her Dryad lineage for example.
Or instead of Unnatural Plants, Unnatural Trees perhaps to be spells/effects which create or transform Trees in unnatural ways or give them distinctly unnatural properties.
I would define Plant Health likely as a major as well. But I'd define it as healing/harming, curing/diseasing, and growing/withering any plants.
Yeah...
You could take a subset of those, or also restrict the plants it applies to, to bring it down to a minor.
Like ... Tree Health, since her interest in Forests and her Dryad lineage for example.
That would work, ofc. But the most useful plants to affect with it are the small ones xD But the thematically appropiate ones would be the big ones...
Or instead of Unnatural Plants, Unnatural Trees perhaps to be spells/effects which create or transform Trees in unnatural ways or give them distinctly unnatural properties.
I like how that sounds, but my issue is that "Unnatural" ends being a very vague term. That invariably leads to too many discussions about when it applies and when it doesn't xD
I prefer something more specific... what about Minor Focus: Animate Plants? It cover ReHe, but just partially, since it only covers living plants and just animating them, not making them move like throwing a tree above somebody or like that.
I think with animation as a focus you could go broader than "plants" and say "Animating Plant Matter" so that it would cover things made of wood or plant fibers as well as whole plants etc. and it would still be a Minor, but that is just my opinion. 8D
That would be the icing xD But i would be happy just with my version I will wait for more opinions on the matter.
Well... meanwhile, with what i have the character sheet (just finishing the Gauntlet) would be something like...
Alba Ex Merinita
Age: 25 (17)
Warping: 0
Size: -1
Personality Traits
Sympathy Traits:
Virtues
The Gift (0), Faerie Magic (0), Hermetic Magus (0), Faerie Background (0), Skilled Parens (1), Affinity with Herbam (1), Puissant Herbam (1), Unaging (1), Cautious Sorcerer (1), Good Teacher (1), Minor Magical Focus: Animating Plant Matter (1), Strong Faerie Blood: Dryad (3)
Flaws
Faerie Upbringing (1), Sheltered Upbringing (1), Social Handicap: Expressionless (1), Small Frame (1), Weak Spontaneous Magic (3), Faerie Heritage (3)
17 spell points left
As long as it only covers animation and not direct control (example: walking trees yes, picking up a tree/log with Rego directly, no) then I think it is a sufficient subset of Rego/Muto Herbam?
16 feels... excessively high for a character just out of apprenticeship. 10 before modifiers has always been a good rule of thumb in my experience. Other than that, I like what I see?
Humm... as written that would be essentially the Level 10 guideline of Rego Herbam, but I think that's not your intent (and alo seems too much restrictive to me).
My initial reading put the following spells from the corebook as valid for the focus of Animating Plants (and none of the ReHe spells I'm not mentioning):
If people thinks that Herbam 16 it's too much to start with, I could reduce it to Herbam 12+3 (using just 52 exp).
Then, lowering Vim to 0 for that single exp point, i could buy:
So... as people prefer. I can adapt 
With Animating Plants i was thinking more in line with the Levels 4, 5 and 10 from Rego Herbam. So, those spells that you said, plus: Twist the Living Tree
With Animating Plant Matter it would also include Level 3. So, to the previous list, it would also include spells like:
Humm... I left Twist the Living Tree out because it doesn't animate the tree, it chages it's position for the duration. And I also understand Plant Matter to include the two spells you pointed out. So, it essentially leaves only wards outside of the scope of the focus (I'm including "Repel the Wooden Shafts" as a technical "ward").
That's why I said it covers a lot of Rego Herbam.
Technically... Wards, craftings with rego, flowers/fruits outside the season and any spell that throw wood or plants around (or turns them into projectiles).
Thanks @Arthur! 
That superpower to move messages is very cool xD
Btw, u haven't given your opinion yet... D: What do you think?
I haven't had time to catch up yet. 
I would slow down if i could... but i must win to Nithyn and Vortigern... xD
I'm pretty close I think...