Is her note still in it?

Yup.

Odd that the person who kept renewing it until she put a hold on it hasn't snatched it up again. Is there anything in the magic section she hasn't read yet? Now might be a good time to circle back to that book on enchanting, see if it isn't more comprehensible with a grasp of the fundamentals under her belt.

The enchanting book is still there. There's also a book about advanced medallion use.

Ooh, neat! She hadn't realized there was more to medallion use than taking fullform and various midforms. She checks out both of those.

The enchanting book says there are three basic ways to enchant: you can enchant an area, in which case your diagram should take up the whole of that area. You can enchant an object, in which case you may either (a) diagram on the object, or (b) lay the object on the diagram while you cast if you need more oomph than can physically fit on the object. You don't wanna enchant a person and this book will not discuss that.

The medallion book discusses the ways medallions hide and alter objects on one's person (especially clothes), ways to affect one's weight disproportionately to how many parts one adds if one's other form is denser or lighter, subtle midform adjustments, why using medallions to heal yourself doesn't really work and how close you can get by not having an injured part, and things like that.

Those are both very cool. She hasn't had much opportunity to mess around with clothes or anything, since she can basically only transform in her bedroom. Ooh, there's a question, does transforming while under an invisibility spell leave you still invisible? There might be something on that in her notes on the invisibility diagram if the medallion book doesn't have it.

Neither source specifies!

Well, fortunately she has this medallion and this invisibility diagram. And the more she thinks about it, the more she wants to do invisibility before enchanting. Invisibility could let Brenda leave the Avalon. It could let Margaret fly. A cloak of invisibility would be even better, a worthwhile sellable enchanting project much easier than medallions but still socially useful, and less reliant on trust than starting with healing. Three days of French incantation design ensue; she also checks the invisibility diagram over for main and residual meanings.

Perhaps unsurprisingly, the main meaning is 'sight', and 'reverse' and 'control' are in there too. Residual meanings are all pretty small.

Margaret takes a lot of notes on how to adapt this to an invisibility cloak, both as-is and one that does inaudibility, but before she actually starts on that she casts the original version on herself with a timer going. (She waits until her parents have gone to bed to try this, since she'd be in rather a pickle if they needed her for something while she was invisible.)

"Make me invisible; conceal me from sight so I may go undetected."

And lo, she is invisible.

And does switching between human form, fullform, and various midforms affect this state at all?

Nope! It could be affecting her duration, but she doesn't have a baseline there.

She'll spend the rest of this duration rapid-fire swapping and moving around her room a lot, then do a baseline where she just sits there in human form afterward. 

It turns out not to affect her duration; in either case she has twenty-seven minutes.

That's long enough that she can sneak out and fly. After making sure there are no sounds coming from her parents' room, she brings a new copy of the diagram downstairs and lets herself out into the backyard. If she stands between that tree and the fence, she can't see into any neighboring properties and that means the neighbors can't see her. Invisibility, emerge from behind tree, fullform, . . . attempt to take off very quietly?

She's not an owl, but she's not that loud.

And if anybody hears her, well, they can look out their windows and see a whole lot of nothing.

Flying is lovely. Her dragon body is long and strong and so much fun to move around in. She's back inside in well under twenty minutes, and sleeps the best sleep she's had in weeks.

The next day she's back to science. If she sets up the water-boiling spell and casts it while invisible, does it mess with the invisibility at all?

Nope!

Excellent. Do things she picks up become invisible too, or only things she's holding when she casts the spell?

Things she picks up stay visible.

What if she takes off her invisible shoes, do they stay invisible or reappear?

They reappear, and don't turn invisible again when she picks them up.