My little girl is 16 months old and STILL not walking!?

Lyla June just turned 16 months on the 19th.She has not yet walked on her own.She can pull herself up by the furniture and even walk around it. I even caught her pulling herself all the way on her sisters bed.She says things like hi mama hi dada ,baba ,sissy,she can wave and say buh bye i even got her a cookie the other day and she smiled and said COOKIE! she does point at things! Her problem solving skills seem to be great she can put building blocks together,turn the pages in a book,she loves to babble on my cell phone..and get down off of furniture without falling...ect..i have been working with her everyday but when i try to get her to walk while im holding her hands she will bend her knees and laugh about it like its funny.Its not so funny to me,though and im starting to get concerned.She is a little petite for her age...could this have something to do with it?