I noticed you mentioned "those" day sleeps. So she is having more than 1? DD was just having 1 day sleep at that age.
I had the same thought. We moved to one day sleep when the same thing was happening. My DS was around 14 months, but the same behaviour. He went down between 11.30 am and 12.30 pm and no sleeping past 3 pm otherwise he would go to bed too late.