I am going to copy one thing of what Ben said, but specifically leave everything else out.
Start making her go to the bathroom every couple of hours.
She has to physically go to the bathroom and sit down and give a solid effort to try and 'go'. I played this game with one of my kids (by game I mean irritating back and forth power struggle) so I get the difficulty of accomplishing this simple task. Every time you ask her to do this she either gives an honest effort or sits on timeout until she does. No anger, no punishment other than timeout, no talking down or treating like a 2 year old. I specifically am against those things and think other answers are off base on those suggestions. Let me explain.
I'm against punishing your daughter for soiling herself. I'm against it for many reasons, but the basic reason is I think it is punitive (eg. avenging, castigatory). Punitive thus means dehumanizing which is something every parent should avoid at all costs. Also, any lesson which has natural consequences really doesn't need additional consequences. Use the natural consequences to your advantage, not your dismay.
To this point I say let her and not you suffer the natural consequences, and thus ease your burden. However, getting her to take the burden of doing that laundry and cleaning up will be a difficult task. However, the end result of that effort is a responsible child. This is much better than a child who feels greater shame and resentment from punitive punishment and degrading talk which will backfire in the end.
1 - She must genuinely try to use the restroom every 2-3 hours
2 - She will be put on time out until she complies
3 - Timeout will happen in public or she will be removed from public/friends etc.
4 - Anytime an accident happens you will focus on your effort to help her be responsible for cleaning up.
5 - If she does't clean up as you determine is good enough she sits on timeout until she lets you teach her how and she does it.
Be patient, guide her, let anger hold no sway over you in this process. Kids have parents because they not able to do things themselves (this includes emotionally too). Keep the burden on her, but always be there to help her become successful in being responsible for her bodily functions and the cleanup when she fails at that responsibility.
While personal opinions may vary among parents on punishment, experts say it is not helpful to punish over accidents. And I do suggest that waiting too long to go is still an accident, which is why my advice focuses the attention on the waiting to go part, not the accident part. This is an important point to keep in mind, you are to focus on the controllable part of the equation (waiting to go) not the uncontrollable part (the actual going).
Potty Training Regression
Experts say punishing your child for bed-wetting or any accidents will
Regression is when the behavior recurs for several weeks, such as when your 8-year-old regularly wets her bed after being dry at night for years.
It may be helpful to consider non medical issue, but rather psychological issues.
Stress is the most common reason for regression.
This fact lends itself to my concept of not adding stress to the situation, but rather letting the natural stress of responsibility do it's work in motivating correct behavior. Finally, taking responsibility is not a punishment.