I am not sure how you are intending to use this in a bigger example, But you should not assemble a function on a different mesh (in general).
Have you had a look at @cdaversin’s Mixed dimensional FEM.
For an example see Stress continuity using mixed-dimensional branch or
https://bitbucket.org/fenics-project/dolfin/raw/f0a90b8fffc958ed612484cd3465e59994b695f9/python/demo/undocumented/meshview-3D2D/demo_meshview-3D2D.py
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