I’m sorry, I don’t know what the timeframe is before the sale is automatically cancelled. Have you checked the last time she was on the site? (Go to her profile page and it will say when she was last on). If it was in the last day or two, I would send her another message on her listing asking her if she plans to ship it. Then if no response, maybe ask again the next day, and if still no answer, I would guess she is not sending it.
Next, if she has sold other items, you should check to see if she has any reviews (if not, most likely she never shipped the items).
I would also check her sold listings to see if there are any comments where the buyer is asking, “Are you planning to ship my item?”
Last, go to her “meet the posher” listing (if she has one) and there may be comments there that help you decide if she is responsive and ships items or not.
These methods are the best way I have to judge. A good portion of items are never shipped or never even in the possession of the seller, but usually at least one of these methods will give you a hint if this seller is legitimate or not.