hi danni- another thing that used to work for my ds when he was your dd's age was to take him for a walk in the pram in the afternoon. i would take him and the dog up to the park for a walk and find that he would drift off to sleep in the pram. then when i got back home i would just leave him in the pram with a blanket over him and would sleep for another 1/2 hour to an hour. not a huge sleep but enough to give you a little break?
now that he's a bit older, if i can't get him to have his arvo sleep i will often give him a breastfeed and then either put him in the car and take him for a leisurely drive around the hills where we live (works 90% of the time) or pop him in my sling while i do some things around the house.
best of luck and try not to 'do your head in' over daytime sleeps. it's hard not to, i know!