That girl runs across illuminated slide (7)
I believe the answer is:
slither
'slide' is the definition.
('slither' can be a synonym of 'slide')
'that girl runs across illuminated' is the wordplay.
'that girl' becomes 'she' (**).
'runs' becomes 'r' (cricket abbreviation).
'across' means one lot of letters goes inside another.
'illuminated' becomes 'lit' ('lit' can be a synonym of 'illuminated').
'she'+'r'='sher'
'sher' going around 'lit' is 'SLITHER'.
(Other definitions for slither that I've seen before include "Slide, slip" , "Slide unsteadily" , "Quietly advance" , "Snake along" , "Move smoothly over a surface with a twisting motion" .)