Artemis has been known to protect maidens. Taking such an oath would show commitment to her. There are a few more reasons why I would make such an oath but I'll keep them to myself.
Yes, but you'll never be a maiden unless I'm missing something.
Secondly, she was a fertility goddess/mother goddess so I'm pretty sure she was down with the shagging and having babies. One could argue that rearing children would be a devotional act in her case.
Feel free to keep your reasons to yourself, but I remain confused.