Should I be concerned?
I would observe in general that many normal children are not yet crawling at nine months and that some children proceed directly from sitting to walking, without ever passing through a period of crawling. There is great variation here. However, if you have concerns about your daughter's development, you can ask your pediatrician or family doctor to make sure that everything is proceeding properly.
Children are wired to grow and to thrive in loving homes where there are ordinary opportunities to interact with other people, to move around underfoot, to play with pots and pans, to watch the fascinating things that occur all about, and (especially) to share the fun with people who take delight in the child's explorations, puttering, and excitement. Standing, crawling, speaking, and listening to stories all develop normally in children--as these milestones have developed in children since the beginning of time. Parents do not need to do anything special, other than to be available, enthusiastic, and supportive of the child's growth. Children come into this world already wired to grow.
I would say, therefore, that there is nothing you need to do to help your daughter crawl. Children are powerfully motivated from the inside to move and explore the world, and will do so as soon as their bodies are ready. The parents' joy is part of the achievement, of course, but the parents are mostly an appreciative audience and do not need to be administrators, teachers, or athletic coaches.
Elizabeth Berger MD