Hello Mr. Versseput,
the trail in general is not difficult, but there are more than 400 steps on metal ladders, so it depends on her confidence with walking on different surfaces.
Moreover, the ladders are made of a metal grill so we know that some dogs can have problems with the feeling of emptiness.
I hope this is helpful!
The walk up/down at the Tempesta end is also moderately steep and on gravel. If I were you I would get the bus to Tempesta and then walk back from there to Torbole.
This also means you don't have to wait for the once per hour bus by the side of the road where there is no pavement.