Lord Shiva is angry god who does not please with beautiful flowers so to please him people offer him leaves of Bel flowers.
Omkara's name is also related to Lord Shiva."Om Jai shiv Omkara" this arti is done for Lord Shiva...
While doing this arti bel leaves are offered to please him..so by this way Omkara and Bel leaves are related...
May be that's why she said unknowingly... 😊