Does Not Crawl

My baby is 17 months old and she does not crawl yet. She started sitting without support at 10 months and getting up by herself at 13 months. Her pediatrician says she has low muscle tone. Slowly and gradually she is developing her muscles strength.

On other side it seems like she is very smart. She understands everything. I would be very thankful if you can tell me some exercises and nutritional food I can use to improve this situation.