How long are you keeping her awake? I found 45 mins to an hour was more than enough, but he was only taking 45 min naps like yours. Someone then suggested because he was only awke a short while( usually 45min-1hr) he would only neep a short nap, which makes sense when you think about it. So i have just increased his awke time to 1.5 hours and he now sleeps for 1.5 hours, it worked like magic. If you are already keeping her up for 1.5 hours and she is still only doing 45 min naps then im sorry i cant help maybe you need to work on the pat shushh method, infact there is great post on the sleep forum that goes into the dreaded 45min nap issue in great detail.
Kelly x