Ashley's not really a good actress. She completely lucked out with Twilight because while the studio knew it would be successful, they didn't know it would become this huge phenomenon. After Twilight's success, they started casting more known actors (Bryce Dallas Howard, Dakota Fanning, Michael Sheen), especially with the whole Victoria recasting. I think the bar was set lower when casting for Twilight but set higher after its success.
I remember reading that she had a manager and agent before she even arrived in LA and thought she was going to be really successful but she rarely got roles. So I'm pretty sure she knows she has to strike while her name is still hot (thanks to Twilight) and she's going to make as much money as she can through crappy films (she's getting $250k per role right now, which is better than $0 because of no roles at all), endorsements (Sobe, Mark cosmetics), and tipping off the paps.
I think she's really smart to take advantage of this. I mean, she used to have to wait tables in between auditions. At least now she's getting lots of $ so if work dries up, she'll be okay.