Thank you very much.
This old lady with the key, how do I get hold of her?
Highly doubt she has a phone or what not - she lives in a hut on top of the mountain (at least as of 8-9 years ago and I doubt much changed).
The guys trying to sell their mule rides to you will know who she is and how to talk to her. (keep in mind you'll have to tip her ofc)
Also make sure you haggle a lot. They will jump on you right when you walk in through the gates of petra offering mule rides etc (just to walk through petra since it is a lot of walking) and you can just keep walking and say you only want to walk and they will keep following you and knocking the price down as you go until it gets to a point you think is reasonable. And if they realize you are interested in kever aharon they will bother you even more since it is quite a trip.
And totally random - but when i wasw there the convenience store at the beginning had a ton of American stuff with hashgachos (pringles etc). Wouldn't rely on it but good to know.