I interpret "whatever I do I must keep my head" as symbolically linking landscape and psyche - it relates the idea of one needing to maintain their common sense on a literal journey into new territory, with the need to maintain ones conscious 'sense of self', of time, and of identity, in the landscape of the psyche. There's almost the feeling that getting lost in this landscape would mean being subsumed by a jumble of images, emotions and events, and slipping into a state of metaphorical 'madness'. The irony is that the statement also suggests a mind within a mind - that she is "keeping her head" when she is already inside "her head". This might even represent the dualism between the conscious, organising mind and the vast, uncharted subconscious mind - where the latter represents the source of both inspiration and of madness.