Don't cry over wet pants....

I have been toilet training Sarah for many years now. Its not something I ever assumed would go quickly so that aspect of it has not been frustrating. In fact it has been somewhat of a relief to see what success we do have as we would like our child to not be dependant on others (at least not entirely) for this function.
Sarah has actually shown some excellent progress and we made the leap to wearing underpants vs. diapers/pull ups recently. She stays dry all morning. We do keep her on a schedule of going every 2 hours. If we go out we have her wear a pull up or when we expect a BM since she hasn't mastered that quite yet either. The afternoons are hit or miss...some days are dry and some are not.
She seems lately to have "relapsed". Its been rather sad and frustrating. Today she had 2 accidents at school! Which has not happened ALL year and almost never happened last year either. I am puzzled. And I kind of felt like all that work....what now!? But I am reminded of how long it took to her to walk...all the practice and what about feeding herself or using a cup. All these things we spent months, years, working on (and still work to improve). So should I cry over the wet pants? No, but I wanted to...but just for a minute.