The Doctor wasn't sure how to feel about Loki. Part of her was intrigued by this "magic" and his curiosity. But he also reminded her of someone else she knew long ago. Her best friend and greatest enemy. Part of her suspected that Loki and the Master were just one in the same.
"What do you think's at the front?" She was curious, keeping herself optimistic as she asked. Something secure was definitely in the basement, and she did really want to know what it was (she loved secrets, but she loved knowing the more).
Plus she wanted to see what this Loki was capable of. As mentioned, she really liked figuring out secrets.