Fully potty trained 3 year old having accidents again?

My 3 yr old had been completely potty trained for over 4 months, she only wore nappies to bed at night and didn't even wet through her daytime nap, but for the past week she has been having up to 5 or 6 accidents a day and today has done both poo and wee in her pants. I dint know what has happened or what to do to fix it....i have returned to asking her 10-15 mins of she needs to go to the toilet, which i had stopped having to do because she was doing it all by herself. Anyone else had a similar problem? Any words of wisdom would be appreciated. Would i be best to put her back in nappies and start all over again or keep persisting with knickers??