Cats purr for lots of reasons: to show happiness, calm and comfort themselves or you, just as a few examples. If she's very new to you, she might be doing it as a way to get up the nerve to play with you, or just to express that she likes you...and of course some cats jut like to purr. You just have to look at my Sybil and the purring starts.
Yeah. Some cats just like to purr more than others. I rescued a neglected kitty I called Olivia and she was starving and sick, and she purred at me anyway so loud I could hear it across the room. She still does that to the shelter people when they come in and clean "her" room at the shelter. Hopefully someday it'll snag her a permanent home. Never met a cat that purred as loudly or as easily as she does. Maybe your cat could give her a run for her money.
Yep, some cats just like to purr. Our Fred purrs all the time, you can wake up in the middle of the night and he'll be purring away, no one's even touching him or looking at him, he just purrs. It's awesome!
All you have to do is touch Julie and the purr-fest starts. Spice purred so loud that the vet had to turn on the water in the sink to momentarily startle her so her heart could be heard. Psy and Bear both purred so loud you could hear them in the next room.