And if she does, go back later with just the information or quotes you want to use, and try to get her on the record. Ask for documentation. Always ask for documentation of what your sources tell you. Present it as part of your quest for accuracy. Or if the source was uneasy about discussing something for the record, say you can attribute something to a document rather than to him.
Documents provide verification.
They may provide details that your source can't recall or did not know. They may lead you to other sources. In addition, they provide precedent. If a source gives you a document when it's in her interest, it may be difficult for her to claim later that the same sort of document is not a public record. Establish a connection.