Yes, i know exactly what you mean.
What I suspect is happening, is that she is catnapping the nap because of the brief awake time.. it's like "I've only been awake for a short time, so I just need a short amount of sleep". This is creating the 45 min nap.
I think you will find if you can keep her awake longer the naps will lenghten. Try 15min every 3 days. I like to extend A time by increasing the nap wind down so that it is low key or take a walk if you can keep them awake. Keep her awake for just the first cycle...if she gets a longer nap then she can go longer in her A times for the next cycle of the day and so on.
If she still naps short, then go w/ a shorter A time the rest of the day and just go w/ the flow. But when the 3 days is up and she is still taking the short naps, extend A time again.
Does that make sence?