the simple ones are cheap on amazon. but they're sized to be wearable while out or for a while making a nice surprise for someone or to show off, which for that they're very fun. If she's looking for a good stretch the larger non-jewelled ones are better.
I've had really good luck with the icicles brand plugs. I've worn them during sex and just out for a trip to the store. They stay in place real well and don't really irritate your ass cheeks at all