If you could use scenes instead of dimming (such as one scene for 50% brightness, one scene for 75% brightness, and one scene for 100% brightness), the Remotec90 might be a possibility. It’s Z wave, battery operated, about the size of a single gang switch in the US. (You didn’t say what country you’re in, but it’s available on both the EU and North American Z wave frequencies.)
This has 8 buttons, and each has tap, double tap, and long Press, so that gives you 24 different options if she has a good enough hand control to do the taps.
I believe @erocm1231 has already updated his DTH so that it works with the new V3 app.
