Jacki's right, 6 months is a hard time for naps. She may well be telling you that she can go for longer A times now, as it is a time for growth spurts. If she used to be able to nap for longer, and the 45 minute monster has raised it's head, that is usually a sign.
I'm wondering if you have tried wake to sleep? If your lo is touchy or spirited like my ds, then pu/pd was too stimulating for him in the middle of a nap. If so, wake to sleep might be the way to go.
Please read the stickies at the top of the Naps forum. There are a few there that would be helpful to your situation, especially: the ones regarding wake to sleep; the sleep interviews with Tracy; and teaching sleep to babies over 6 months+.
I hth, remember we are always here when you are tearing your hair out, and want to scream into the pillow and bang your head against the wall, b/c we've all been there