In most cases, once a tentacle beast is done with the victim, the two become merged, the victim joining the the beast in a mass of tentacles before slithering off back to the realm between worlds. However, the beast was a bit outmatched by Helen's willpower. Yes, the Society's scientist did end up reduced to a writhing mass of tentacles, and yes she did become absorbed among the beast's slithering limbs... however, she did not become subservient or dormant as the other victims had. In fact, her mind soon overpowered the beast.
We aren't sure how or when, but at some point the tentacles began to twist and swirl together, their morphic chaos nature allowing them to shift and reform into a semi-familiar shape. In time, Helen became whole once more... although with some noticeable changes to her physiology. She could split her limbs into masses of tentacles, grow new slithering limbs from her back, and many other inhuman factors she claims to still be researching. While the Society is relieved that they hadn't lost another scientist... they have become concerned with her sudden obsession with studying the reproductive habits of Tentacle Beasts... and her most recent lab assistant has gone missing as well...