Hi NarrowJ,
It is usually one of the below when that happens:
1) Shes not really interested in either you, or the topic you're talking about, and is avoiding to give you answers.
2) Bad timing. Shes busy.
3) She is generally like that with most people.
So depending on how well you know her, you need to react differently, and it is also subject to what you're talking about too.
Ignoring would be best.