It's an interesting question, since during Dixon's BoP days the holograms were quite insubstantial and various Bats at various times walked right through them. However, in the BATGIRL title, Cass invariably used them as Danger Room-style interactive environments. Perhaps Cass merely has such insane control over her body that she can stop a kick "on impact" even when it doesn't hit anything and accurately simulate impact to herself in her own movements when an illusion punches her. It honestly wouldn't be the most absurd thing her body-reading let her do by half.