If she's stopped purring so much she might be recalling stressed, anxious or unwell. How's the rest of her behaviour? If she's absolutely herself in every other respect (still eating, peeing, pooping and playing as normal) and seems as relaxed as usual there probably isn't anything to worry about. If there are additional behavioural changes, though, there may be something going on with her.
Some cats just purr less than others, or sometimes just don't feel like it! When my boys first came home, they'd pretty much start purring as soon as I touched them. Now we've had them for a few weeks and they're a bit older, one of them purrs MUCH less. To me, this just makes the times when he does purr for me extra special