MSP, I'd suspect you're right on track with something being better than nothing. And if she wants an option more tailored to her preferences, I'd say it's up to her her to take the initiative with that.
Growing up, in my family you either cut your own hair or you hand the scissors to someone else and don't complain about the results.

It's just hair, it grows back. Good stories come with the territory.

We never "announced" any drastic cuts to one another, we simply emerged from the bathroom with a new look (and occasionally a smug accomplice). My mom, sisters, and I got most of our practice bloopers worked out when we were pretty young, and honestly I'd trust them before any professional with it because they don't have any high notions of giving me something fancy they
think I want when it's not what I asked for. I still prefer the scissors in my own hand, though.
I've never cut a short hairstyle on someone else before, but as long as they didn't mind the potential for a botched result I'd welcome the opportunity. I guess a lot of it is personal to what someone feels is DIY and what should be reserved for trained professionals. I can see how a person might be nervous about cutting hair if they felt it required professional training to do right, and especially if their own image is so wrapped up in their hair that a botched cut would be disastrous to their self esteem. That kind of thing is pretty easy to project.
MSP, have you considered having a go at it yourself? I'd think that even if it goes less than spectacularly, if you just up and decide to stop getting professional cuts then eventually one of you will learn how to do it acceptably, and if she sees you messing up that will be more motivation for her to step in.
As for instruments, we always had haircutting scissors that are never used for any other purpose. They're generally the sharpest pair in the house. I currently just use regular scissors on my hair, which is inconvenient enough for me to be on the lookout for getting some designated ones. My family also has some thinning scissors, which I think have been used once or twice in a decade or so. A fine-toothed comb is also useful if you want to make sure the ends don't appear raggedly.