Dont get discouraged mama! She's almost there!
DS was a "late" crawler. Late in quotations because really, it's in the realm of normal, just not as early as we all wanted. Like if the range is 6-9 months, don't we all want them hitting those milestones the day they're 6 months?
Give her lots of encouragement. She could learn to crawl, pull up, and cruise all in a month. Really!
DS has really only gotten good at crawling on all 4s (he did tummy/army crawl for a while) for like a month or two. It's really not been long. Then he figured out how to stand on his own, and now he's attempting to walk. It all happened like bam, bam, bam, one after another!
If she doesn't hit the milestones when your pedi wants her to, it's not bad to see if there are some ways to help her along. Not sure if it applies, but my son has had alot of food milestone issues, and it seems that a couple ear infections really had an impact on his eating. Is she good and healthy? Think about when you have a sinus infection and you bend over... ouch! I wouldn't want to crawl when feeling like that.
Otherwise, be patient, help her practice, encourage her, and she'll do things when she's ready :)