Both of those work. Their meaning is not all that different in practice. The second is more ponderous and probably less in use than the first.
You certainly don't have to use either of those (in answer to your question 'do I have to...?').
It's English: there's always another way to say/write things, some better than others. Substituting only for the second sentence:
- 'Was she lucky or what?' (implies that you are fairly sure she was lucky).
- 'Might luck be the reason?'
- 'Could it be luck?'
- 'To what might we attribute this? Luck?' (also a bit ponderous)
- 'Dare I suggest luck as her secret helper?'
I'm not suggesting that any of these are better, or worse, but they are alternatives. Doubtless there are many more.