I was having major problems with 45 min. naps, until I realised dd was on a growth spurt that was lasting longer. How old is your dd now? Have you always had 45 min. naps or did they start a few days ago? How is she fed?
With my dd I just started breastfeeding her when she woke, she would take a full feed and then I followed her cues for sleep. sometimes she would start yawning 10 minutes after eating and I would put her down then, she would sleep 1.5 hours straight. Once the gs was over, her nap issue resolved itself.
One thing I would also suggest, if you rule out the gs and hunger, is going in at the 40 minute mark and help her transition to the next cycle without her having to wake up. As soon as she stirs you can pat, shh, apply gentle pressure on her body to prevent the jolt, or any combination of these.
Keep us posted, HTH
Sara