To add to place suggestions:
Blackwoods of Rannoch has some nice chilled and very wild/remove feeling bits, we did a few loops with the boys there.
Loch Voil – road down one side, over the stepping stones at entrance of Loch Doine, back down the track (one bigger climb). Feels like a proper adventure, even though it is half on road.
It may seem silly, buuuuut, start the Ben Chonzie ascent? You can go as far as legs will agree with, sploosh in a few streams etc, and roll back down when she has had enough.
Lady Mary’s walk along the Earn from Crieff was a favourite of the boys when little. Go up road and farm track, down with the river.
Know anyone in Callander? You can go from Killin to Callander, leave her at a friends place and pedal back or get bus back for car. Mainly downhill. Again, the lads loved this ride. Beavers en-route now as well.