Oh girlfriend, I hear you! My son (who is now 21 mo.) was and still is the same way. 45 minute naps was about it 2x a day. And now, he sleeps once a day for about 45 minutes and if we're lucky for about an hour and fifteen. He sleeps about 11 to 12 hours a night. I did talk to my doctor about it when he was about 6 months, lamenting that everything I tried, (which, by the way, was everything you tried) didn't work. She just laughed and said he just might be getting enough sleep already and may not need to sleep any more. She said that the important part was keeping a routine consistent.
I noticed that your baby is still taking 3 naps a day and might be in transition and ready to eliminate one of them. Maybe move the first nap (at 9am) up to say, 11am? And then move her afternoon nap to around 3? And no third nap...Just a suggestion.
Hope this helps! Good luck!