Where do you have her sleeping? I would try the room darkening blinds/curtains and a white noise machine for her. If she wakes up at the 45 minute point go back in lay her down, ssssh her and leave the room and leave her in her playpen for the remaining nap period.
I have one in my care who is 16 months, she recently started waking at the 45 minute point then crying for 15 minutes, falling back to sleep then waking up again. I will go in once and lay her back down but then she stays there for the remaining nap time.