Bubble Over Meaning

Example :   She was bubbling over with laughter as she ran into the room.1909, Archibald Marshall, The Squire's Daughter, chapterI:  They stayed together during three dances, went out on to the terrace, explored wherever they were permitted to explore, paid two visits to the buffet, and enjoyed themselves much in the same way as if they had been school-children surreptitiously breaking loose from an assembly of grown-ups. The boy became volubly friendly and bubbling over with unexpected humour and high spirits.