I have to agree with everyone else, that she "looks" pregnant, but as for how far along, that's a bit of a "how long is a piece of string" type question. My guppy had fry about three weeks ago and is "technically" due again on Monday, but she's not fat, has never been fat, but she does have a dark gravid spot like yours.
As for how long they can go between pregnancies, that's really up to the fish! I had one of my female molly's for nearly 5 months before she finally decided to have fry!
Make sure your water quality is A1, do extra water changes, maybe do one mid-week, and feed the best quality food you can afford, along with live/frozen foods and vegetables.
Really all you can do is wait, frustrating I know, drove me nuts until my first female had her fry.
And they're small too, around 3 - 4mm, sort of transparent with a huge set of eyeballs,which means you may not see them at first either! They are as quick as a flash and very good at hiding!
Good luck, it's the best feeling finding your first batch of fry