I'm not sure the RSPCA would be able to do anything (not that they don't care but I don't think there's any legal restriction on how long you can leave a dog as I remember someone checking over a puppy). They do have company at least and shelter - but I would worry about how their staffie coats will cope with the cold weather if this is a long-term plan.
Have you had a chance to chat with the woman? Who knows what has led her to this, perhaps while it's not ideal, she's doing the very best she can for the dogs right now and would be grateful for some support/offer of help if you're able? Am guessing you are home all day to know that she is leaving them unattended all this time and not coming back at lunchtime, so could you offer, as others have suggested, to go in and see them?
I know you shouldn't have to but if they're friendly dogs and the woman said yes, it might be better for all involved, you included, if you could help? You might find out why they are outside and hopefully you'd be able to better judge the situation before doing anything further?
Plenty of people seem to go out and crate their dog during the day, or leave them in a small room, with a break for lunch. At least these two have a bit more space than a crate and they have each other for company. As long as she's not leaving them out there 24/7 and she's giving them her time and attention when she is home and she's usually leaving them 7 rather than 13 hours a day(?) ...
It's good that you care and are watching out for them and I wouldn't want to leave my own dogs in that situation, nor approve a home that did, so don't think I'm saying this is ideal, I suppose I'm just thinking she might have a valid reason for it.
p.s. lovely to hear you have adopted a new doggie friend - have we had an introduction thread?