If she can reach the dummy herself and put it in then its not considered a prop but a comfort item and is perfectly fine, she may be waking up for another reason if she doesnt really need it to fall asleep, how long is she awake for before going down for a nap? usually waking up happy from a 40-45min nap means she went to sleep undertired and therefore isnt tired enough to do another sleep cycle, if she wakes up and is grumpy/crying /irritable then its likely she needs more sleep, if thats the case then i have a gently weaning technique that you can try and I know it works because I help mothers with it all the time