I have a few thoughts on this, which may not be cohesive because I was up all night--but here goes, anyway.
I think that asking an employee--regardless of her background--to administer testosterone injections is wrong on many levels. On the most basic, yes--it is asking her to put her professional license on the line and, if she's no longer practicing nursing, and not carrying malpractice insurance, it can cause problems for her. (No, I don't think your husband would sue her---but people DO sue, and anyone with a professional license is acutely aware of this.)
A layperson administering medication at someone's request can rarely be held accountable if something goes amiss. A medical professional can be held liable--often disastrously so, and often unfairly so.
But really, the odds of any adverse reaction to testosterone or its injection are slim.
Things that raise my antennae are:
1. The woman is a subordinate, so there is a power imbalance; that she consulted her lawyer brother about this indicates, to me, a level of discomfort, a desire to find a way to STOP this non-job-related duty.
When you're practicing as a nurse--and by this,I mean in a healthcare setting---boundaries are firm. Yes, you deal with intimate things, touch bodies, etc. But there are very clear boundaries.
When you're administering testosterone to your boss in a non-healthcare setting, those professional boundaries are blurred. She's not primarily a nurse; her role is something else. The waters become muddy, because in order to safely administer the drug, she MUST know the correct amount for the intended purpose. She MUST know what she's injecting, and why. She MUST have information that, really, a female work subordinate should not have.
She was smart to stop. Even if your husband was not thinking of you, it's quite possible SHE was. Or, she may have just felt weird about it.
I know I did, when I gave a (female) colleague injections for MS when I was working in a non-healthcare setting. I have NO problem with the necessary intimacy required when providing patient care; asking intimate questions and touching bodies is very different in that role/setting, when boundaries are firmly in place (as they are, for most of us, all of the time0.
It's just kind of hard to sit across the conference room table with someone who---in order to assess the effects of the drug I've administered---I've just had to ask whether the urinary incontinence has been impacted by the dose change. (Because no nurse just gives an injection. We MUST know the drug. We MUST know for what it was prescribed. We MUST know the appropriate dose, and we MUST know the appropriate route of administration. And it doesn't end with injection. We also MUST evaluate the treatment. Because we DO put ourselves on the line when we agree to introduce any substance into another person's body.)
The intimacy required for administering nursing care---even something as seemingly small as giving a shot--impacts relationships. When there is intimacy in one aspect of the relationship (and again, even giving a shot requires sharing private information, and physical contact), those lines can get pretty blurry.
2. Rational or not, we ascribe a great deal of power to testosterone. It symbolizes virility, masculinity, sex. It is emotionally charged. Your husband unwisely chose to give a woman who was not his wife--and apparently is not even working as a nurse currently--a window into his life, make her part, albeit small, of his masculinity, sexuality, well-being. It was inappropriate.
3. This woman has talked about your husband's personal information with at least one person (her lawyer brother--unless that is just a story she used to get out of doing something that made her uncomfortable). Not good.
4. Administering injections is not rocket surgery. My kids could do it when they were in elementary school. (Their father uses insulin.)
Your husband is an adult. Is there a reason he is unable to administer the testosterone himself? There are many sites that can be easily reached; the thigh is especially good---it's often overlooked, but a great site because of ease of access, large surface area, and relative paucity of nerve endings.
If he is squeamish about it (and some people really are), you can give them. There are tutorials on YouTube and elsewhere online. If you would like more training, I guarantee his doctor would be delighted to have a nurse or patient educator teach you. You can do it