And if something were to happen to her—say she had a bad reaction to the medication or developed a condition, possibly even a life-threatening one—she’d likely be the first to sue the doctor who prescribed it to her husband. Naturally, her husband would be fully on board, supporting her in suing that “mean old evil doctor.”

And that, ladies and gentlemen, is one of the reasons our medical insurance premiums are through the roof! Way to go SD and husband of SD! 

In some cases, maybe what you said is the best possible outcome when you wrote: I may not have to worry about our wills, but we will probably outlive her due to her stupidity.  

Though I am team "the doctor works for me",  am also a data and research focused consumer of medical services in the treatment of actual Dx'd conditions and not the "I saw it on YouTube" condition of the moment idiots.

I have been on those meds for just over a year. 10  years ago I was on the first iteration of the gastroperisis inducing meds. It was called Byetta.  Fondly referred to as Lizard Spit.  It was identified by research into Gila Monsters to determine how they could go a year or more without eating.  An element of their saliva slows digestion extensively allowing for their metabolism to digest food slowly which the pharmaceutical/medical industry determined is a benefit to normalizing blood glucose in diabetics, My Rx has been off label since it is specifically prescribed for T-2 diabetics. As a T-1 there is risk of dangerous Hypoglycemia if not carefully managed as part of the comprehensive treatment regimen.  

If she is taking the stuff without direct medical supervision the risk of negative outcome is significant.  My Endo is titrating me up the the max dose on a 1+ year titration schedule.  She bumped me from 7.5mg to 10mg on my last visit with her in early Dec.  I have been at 7.5 for an extended period. I asked if we could go directly to 15mg.  One injection a week.  Nope, she said going to the max without titrating through 10, then 12.5, ultimately to 15 could be decided unpleasant and dangerous with a significant risk of hospitalization. It basically can paralyze your GI track and resulting in debilitating nausea and a severe risk of systemic toxemia.

The orignial lizard spit worked great, It was a daily injection and titrated from base dose to max dose over about 6mos. The problem was that about 10mins after injection the most horrendous nausea imaginable would hit and last for about 15 mins.  Nausea and inability to throw up to relieve it.  So, I would take it, just before bed, gut through the nausea, then pretty much pass out for the night.

The way it works for me in the modern formulation is that the nausea starts after about 2days and is intermittent for a couple of days with waves that pass in random frequency and duration for the two days.  Pretty much I am not hungry.   It does drive weight loss but once you adapt to it at the 7.5mg dose it is not unheard of for people to return to their usual eating habits. Overeating on this stuff is decidedly uncomfortable.

So, if SD is stealing her DH's meds mixed with her proven level of stupidity, I forecast the crying call for daddyyyyyy to pay her hospital bill when she paralyzes her gut and ends up feeling worse than she could possibly imagine.

The lesson needs to happen IMHO.

Stay away from helping her when she nearly kills herself.

As for "those types of people", my nephews wife has decided she is not mentally ill and has some physical ailment rather than a psychological one.  Of course actual doctors have done every test and Dx assessment possible and there is not a damned thing wrong with her physiologically.  But, she has a Master's degree in an engineering field and is smarter than the docs. This is is the one who knows more than the top companies she has worked for and leaves riding on her high horse when she has had enough.  Sadly that leaves my nephew the some earner and subject to her bullshit. But I digress.

SD is likely in for a decidedly unpleasant experience on the semaglutide theft and use idiocy she is stepping into.  I see her thinking that she needs the max dose and may "take 2" because she is frustrated that she did not lose a hundred pounds after her first injection.  She is in for misery beyond comprehension if that is the case.

Even I asked about it. Fortunately I am aware enough that while I am the world's foremost expert on "my" disease I am not the worlds foremost expert on THE disease.  I listen to the people I hire to work with me on managing it.

This is dumb. Maybe (if she manages not to kill herself by taking the inappropriate dose/having a bad reaction of some sort) she might lose some weight. But then what happens when the supply runs out? Unless she completely changes her eating/excersize habits she'll just gain it all back without an ongoing prescription. 
 

And she is 100% full of sh- about the doctor letting her finish someone else's prescription. There's probably a host of legal and insurance issues with doing that. 

It takes a special kind of stupid to take something that is prescribed for someone else and imagine that everything will be fine. Meds are not one-size-fits-all. Many years ago, my MIL had a headache and, not having the usual OTC meds, took one of the pills prescribed for his intense, recurring migraines. She woke up in the ER. Let's not think about what would have happened if somebody hadn't gone home early from work that afternoon. 

H. asked if her reg. Doc is okay with that.  SD says Yep!  No problem, she should finish off the perscription.

There is absolutely no way a doctor would tell her that. First of all, you are right, it is illegal to take prescription medication that is prescribed to someone else. Second, he refused to prescribe it to her in the first place, so why would he tell her it was okay to take her husband's?

She is definitely lying.