WTF. In what legal systems does that work?
For example, if this was in the US, did the woman plead the fifth, or did she assert to something she knew to be false? Was she convicted of a crime and found to have knowingly concealed having committed the crime? Did this conviction come before or after her lying on the stand?
You assert your innocence by pleading innocent before a trial takes off. Not by obfuscating on the stand. If an option is to not comment on your innocence under oath, or you'd be lying if you did that, then don't take the stand or remember you don't have to admit to a crime. But unless there are provisions against what lies are applicable to perjury I don't understand how it wouldn't be perjury