When Interrogator-Chaplain Boreas and his squad go aspirant hunting in the Angels of Darkness novel he breaks the neck of one of the three "winners" of the initial tests because he chickend out when the apothecary had to go poking about in his tummy with his gear. Well, he didnt kill him because he chickend out, but because he'd seen to much of the chapter and the astartes, and this was still on the kids home planet.

So let's break it down.

First, the girl in question have to make it far enough in the initial trials, be it gladiatorial combat or whatever.

Second, the initial apothecary tests, and here she's busted. What would hapen to her then? Well' depending on chapter it could be anything from serf, mindcleansed and made into a servitor (for use in the apothecarium or librarium perhaps?) or just, as in the example stated above, killed and burried and honored in a seecret cave with other failed aspirants.

All likely.

But the Dark Angels are super secretive even by Marines standards.

So it's not impossible that others may be a little more magnanimous

than simply killing.

Realistically its a matter of chapter. Ultramarines recruit from things

akin to Greek gymnasiums, so nudity is likely making subterfuge almost

impossible, and if caught Ultras are more civilian friendly so less likely to kill.

Blood Angels may be easier for such to happen, what with the full body coverings,

but more likely to make a chapter serf than a corpse or servitor out of anyone who

can survive the trials. Same could probably be said for Space Wolves given

the crap their recruits go to in order to gain notice.

Dark Angels are secretive and may kill or servitorise them like any other failed

aspirant.

Black Templars have a rep as nutters for a reason and may kill or servitorise

out of hand claiming blasphemy, or view the individual as exceptional and somehow

use them as a serf. Given the level of freedom given to each crusade fleet any action

is possible based on the circumstances, apothecary and chaplain involved.

And the Storm Wardens, Emperor alone knows.