She also leaves her art in abandoned buildings, like these. This could be an exception to the leave only footprints rule of exploring. Besides, these would harm nothing and they are not permanent.
Just because street art is a relatively modern development doesn't mean that it should only feature modern artistic styles. NeSpoon, a street artist in Poland, creates beautiful pieces of street art that imitate traditional intricate lacework. Nespoon doesn't limit herself to just spray paint and stencils, either - she also uses cement and actual crocheted lace.
Source: Polish Artist Covers City Streets In Intricate Lace Patterns | Bored Panda