I don't keep links to MSM hand, and I do understand why you're asking if that's a safe assumption.
Here's a link to an earlier post with a list of case cliff notes that were sourced from an article on MiltonKeynes.co.uk site
UK - UK - Leah Croucher, 19, Emerson Valley, Milton Keynes, 14 Feb 2019
And in there it says about the family home being Quantock Crescent. And that Leah walks from there to work each day.
I haven't seen/heard anything to suggest Leah didn't start off from there on the day she went missing. Buzzacott Lane isn't that far into the journey so it seems a safe assumption that she did start out from the family home if we don't have evidence to state otherwise?
I don't think we've been told much at all really, but I don't think there's been any suggestion that Leah was particularly early or late that day nor that her starting off point was from anywhere else. I think it's just that the initial police report would have been that the last sighting by her parents was on the evening of the 14th, and then LE found the cctv of her on her way to work as normal.
ETA I've changed the word in my last post to 'implying' as I feel that's a fair word for it, but you're right that I don't know if it's been explicitly said that way.