My DS had a patch of accidents about a month ago after being TT for 6 months. It coincided with a huge leap in pretend/role-playing type of play, he was just so engaged in his activity he was ignoring the urge until it was too late. After three accidents in one day I cracked it and made him wear pull-ups for a couple of hours - problem solved!

Maybe try asking her a bit more often just in case she is forgetting to go.