I would say "sure"...go ahead with the version she is comfortable with. No version is perfect anyway. Lots of truth in the NWT, but whatever book you are studying together, I would have at least one other translation handy for comparison purposes.
Besides, the extra-biblical teachings are already in her head; so she will be bringing WT interpretation to the text anyway. I would not challenge/contradict her on the extra stuff she adds but just say that you don't see that in the text but you are willing to hang that idea on a hook for now and go on. No good jumping around to questionably related material.
Here are the rules I let Witnesses I study with know beforehand.
GUIDELINES FOR VALIDATING DOCTRINAL CLAIMS
There must be at least one scriptural reference that can
cited for support of any doctrinal claim or position.
Scriptural references must not be tampered with
to, deleted from, or have words substituted or
Scriptural references are considered arbitrarily linked
it is shown that subject or content is clearly related.
Interpretations of biblical passages must take into
context, including textual, situational cultural and