>I believe Ashley's mecha-summons are unique. Why should there be a book about them?
All creatures on the negative plane are as varied as creatures of the material plane, all planes are parallel.
Ashley's summons are demonic or material in part and where they were originally necrotic in part, they are now mechatronic in part in terns of what she can summon though she may not be limited to that always. The necrotic summons exist in the book and those are governed by the raven Queen, and any other creatures that would have a mechatronic part are governed by the mechathereal demigoddess. The question you are asking is answered by saying several difficult concepts.
1. Time does not pass on the other planes the same way as it does in the material plane, it can, but it doesn't have to.
2. Creatures created on the Negative plane that are mechatherial in nature could therefore be documented in this book in the material plane because: time doesn't work the same, from the material perspective all the negative plane's history is discoverable. Same is true in reverse. Also, the age of the mechatherial demigoddess is unknown, when she arrived or departs from the negative plane is immaterial.
3. Only 200 spells exist in this book, it's a tiny subset of all possible creatures on the negative plane, but being a sorceress, Ashley can take a part of one spell and add it to another.
For instance, necrotic-giant-rat: from this she could learn to summon a rat, a necrotic rat, or a giant rat.
Given she can summom a cat, using those parts of the spell, she can learn to summon a necrotic cat, a giant cat, or possibly even a cat-rat.
So of the 200 spells, their combination in conjunction with creatures on the material plane can combine to summon near infinte combinations. So at this point, if she saw a necrotic rothe in the book, she could piece that together with her latest spell, the mechatherial panther, a summon a mechatherial rothe.
This differs from Yulya's book where she has only explicit spells from tier 1 to 9 that she copied there as a roadmap of her divine path.
>Can Ashley even summon these abomination now that her connection to the Raven Queen is cut?
The connection to the Raven Queen allowed her to summon, and in addition, summon from a class of creatures, necrotic. Her connection to the mechatherial demigoddess allows her to summom mechatherial creatures. Given what she learned from both schools, she could technically summon anything that she understood previously, so she could still summon necrotic things, and normal things.
In essence, she is summoning named creatures' souls that are known to her, these creatures exist in negative plane bodies and are popped out of that plane and into the material plane in material plane bodies, not the same one every time. Note: Mechathereal hybrid bodies have certain benefits over standard material bodies just as necrotic hybrid bodies did.
>stinky undead
Ashley doesn't like stinky undead things and she wouldn't do that if she didn't have to. You could say her summon spells are like phrases where she can choose suffixes and prefixes or none. It's her choice as long as she's capable of summoning them. At this time she can summon up to CR1 creatures. Nixie is technically a CR1 creature but I may have mislabeled her because the original panther is CR1/2
A standard rothe is a CR of only 1/4 but the greater heavy rothe was a CR of 4. She could conceivably summom a heavy Rothe for CR1, considerably weaker than the greater heavy rothe
In addition, she likes cat things, so her summons will generally have that flavor but it's a preference. She may attempt to summon any sort of monstrosity in the learning of her next spell up to CR1, and that research will culminate in the summoning of a creature of high strength or a beast of burden when she reaches level 4.
