My friends 9-10 month old is not crawling yet - what advice should I give?

Hi there, I have a friend who has a 10 month old that is not crawling yet- she does have the ability to roll to get to things, can hold up head on her own, but doesnt know how to get to a sitting or crawling position. I want to give advice, but as a First Time Mom whose kiddo is now 3yo and didn't have this development delay. What advice could I give? The 10 month old did have slight weight gain issues the first couple of months since then has been great! Any ideas for helping baby get to these next milestones for my friend would be appreciated!