Posted: 04/04/2014 at 12:20
Trees don't like being underplanted, so the usual advice is to leave a bare patch around them anyway. If your neighbour hates that look, then she could cover the ground with an attractive mulch, which will eventually feed the tree anyway if she uses compost or chipped bark; but using pebbles etc would look better than bare earth.
If she's intent on planting underneath the trees and is prepared to keep watering there, then she could try grouping large containers under them (ie too big and heavy for thieves to take) with appropriate planting in them for the shady conditions.
For cheap front garden hedging, I'd recommend buying appropriate bare-rooted roses - good prickly stuff to deter unwanted intruders. Alternatively, make friends with someone with shrubs that need regular cutting down hard and use their prunings as cutting material to grow your own hedge.
The tall coloured stems of dogwood (which needs to be cut right down in early spring every year) will root almost everywhere - encouraged or not - and will grow as lavishly as the parent plant in only a few years. Meantime, they'll darken slowly from their initial bright red or yellow colour.