User blog comment:DeathGodPrayer/Talk About What You Want!/@comment-98.77.247.232-20120706215031/@comment-5185939-20120707040854

Never said she wasn't, just that she's allied to an enemy/rival in Vali, and that said enemy/rival is also a Devil who could contract with her. If she left the Vali Team, then I could see her contracting with Issei.