Well, has anyone thought to find her doctor & ask these kinds of questions? There must be a doctor involved: Adderall, & the better-known drug for ADHD Ritalin, are both Schedule II drugs which one can only buy with a doctor's script. And if you can find a pharmacy that not only carries it, but has it in stock. IMHO it's easier to buy meth -- which is illegal than it is to buy Ritalin -- which is a Schedule II drug.
And by "anyone", I'm also including agent Velling. I don't think doctor-patient privilege survives the patient's death, & if the inquiry from LE is based on identifying the patient, I don't think any reasonable doctor would refuse to cooperate. And having a professional opinion/diagnosis about LEK's medical profile -- if she had something like Marfan syndrome, or if she had ADHD, etc. -- would save us a lot of guessing. And if Velling did get a medical profile of LEK, whether or not that is shared with us, would allow us to eliminate some possibilities based on an argument from silence. For example, it would allow us to consider it reasonable to assume she didn't have ADHD (as I wrote above, Adderall & Ritalin would require a diagnosis & prescription), & those pills Blake reports she was taking might have been something innocent such as over-the-counter medication like aspirin, or vitamins. Of course, if we knew that we'd then ask why she was obsessively taking pills: was she a hypochondriac?
And if Velling never talked to her physician, then that is a lead someone in LE needs to follow up on. Many medical conditions are based on genes, which would help narrow the possibilities.
(And if Velling had that information, but either was holding it back for various reasons or I missed reading that, then I'm just showing my ignorance again.)