My impulse here is to go for total coverage—something that will go up and even cover the fence above the wall, thus producing a homogeneous surface as a backdrop. There are some largish climbers you could use for that. Some of them will self-cling and round themselves around the texture of the wall. I’m thinking things like Schizophragma or climbing Hydrangea, a large rambler, Clematis armandii, Ampelopsis megalophylla.
Thanks @Cambridgerose12, climbing hydrangea or ivy might be better, it's got to be something that's not poisonous to livestock, there's sheep in the field above. Also my daughter doesn't want anything that needs a lot of maintaining, she's not a gardener yet and the wall is very high.
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