I would add, that it is possible she could get the nomination because people so often assume that she can't. She can win, because people won't take her serious until it is too late.
3. The other candidates are flawed.
4. The other candidates might not run.
5. The media will be rooting for her.
6. She's tough to campaign against.
7. There are virtually no moderates left in the Republican base.
8. Attempts by the Republican Establishment to neuter her may backfire.
9. Parties tend to nominate more extreme candidates in elections against incumbents.
10. She gets new media; new media gets her.