They dumped her in a backwater universe because leaving their test subjects in the same universe but with altered memories would have been leaving a huge piece of evidence that anyone with the proper stuff could find; Talvi's entries have demonstrated that mindwipes aren't foolproof, and since it'd be obvious something suspicious was up -- bunch of kids vanish inexplicably, turn up weeks later infected by neoshadows and seemingly-unaware that anything had happened -- there'd likely be inquiry, and at some point someone would try a memory drug, at which point every single kid would independently point them towards Ballpoint (one kid could have been false memories, dozens of them all corroborating each other is almost certainly something the authorities would look into). So, they abduct the children from somewhere, perform the tests they need, and then,
after they had finished with the tests, mindwiped the survivors and dumped them somewhere random where they wouldn't make trouble, possibly implanting tracking devices into some of them for long-term observation.
They probably didn't really care where they sent the kids afterwards, as long as they couldn't reasonably be expected to come back and testify; Rose (one of dozens, perhaps hundreds of 'dumped' children) just happened to end up at Spearbreakers.
Subjects would be enclosed in an isolated holding cell to keep things controlled and scientific. The cells would have been metal-lined to prevent the neos from phasing through the walls and floors and any egress points would be equipped with multiple high-grade floodlights to destroy any neos that try to break out. Tests
I personally would like to perform on someone with such an infestation they likely performed include:
- General physiological stuff: How does the neo's energy-leeching impact the host's bodily functions? They'd likely have performed general endurance tests, likely along with exposure to temperature extremes to test thermoregulation, tissue samples to see the extent to which cell growth is negatively-impacted, and extended food deprivation to see how lack of energy intake of the host affects the neo.
- Immunology: Does the neoshadow, as an invasive element, generate any sort of immune response, or for that matter inhibit normal immune function? Blood tests are likely, along with deliberate exposure to pathogens.
- Mental functioning: Does the neo's interference negatively impact the host's thought processes? General aptitude tests are likely.
- Emotional bonding: When attached to a sapient host, will the neo develop a personal bond with them? Are neoshadows social creatures? What sort of relationship would the host form if the parasite they're infested with can converse? Tests would likely involve introducing agitated animals to the holding cells to see if the neo defends a sapient host more aggressively (which would indicate an emotional bond) and leaving the pair in isolation for extended periods of time to see if they converse.
- Obedience: Can the neoshadow be trained to accept commands from its host? Likely would involve placing a desirable object out of reach of the host and having the host instruct the neo to lift them up so they could get it, possibly with some sort of punishment should the neo not cooperate.