Funny thing, but between 12 months and 2 years some kids who were previousl. good sleepers NOW start to give us the odd problem..
I guess you'd want to rule out teething, ear infection etc. first so you could either take her to the ped. or try some pain medicaton. Any other changes--a new programme, playgroups etc?
Is she on one nap or two? Nightwakings can indicate an "inappropriate" sleep schedule which is pretty common around this age as some lo's start getting ready for the one nap tranistion around now. Sometimes what happens is that they start taking naps later in the day and it impacts their ability to fall asleep early at night. Too late bedtimes inevitably led to night wakings in my younger dd.