First I'd take her to her pediatrician and get her checked to be sure she doesn't have a physical issue. She could even have a urinary tract infection that isn't hurting but is making it hard for her to stay continent. (yes, little kids can get those.) Don't make her feel the dr. trip is a punishment or is being done because she's failed but be casual about it.
I'd talk to the dr. in advance too and be sure the dr. will have a talk directly with her (if there is no physical problem) about how she can do this, she is big enough, etc. -- not a scolding talk, though; you want to build her confidence, not reduce her to tears and frustration. Some kids listen better to an authoritative adult other than a parent.
It won't be the only solution but might get her attention for a day or two that you can then spend buckling down and getting her to stick to the schedule of "we potty when we get up, after breakfast, before we leave the house, when we arrive at (store, school, grandma's), before we leave there, when we get home..." etc. Lots and lots of praise and rewards when she uses the toilet.
I think your idea of these kinds of set times is a good one. But be firm without showing your own anger. Remember, one thing we cannot really force another human to do for us is use the bathroom. It's hard to say if she is still having trouble stopping her playing etc. or if this is a control/getting mom's attention issue, but it sounds like the former if she's upset rather than defiant about it. She probably is picking up on your anger and frustration, which feeds her own upset, and if she's upset it will be harder for her to read her body's signals.