[OMFG!You'reActuallySmart!]

Since she is in a higher position than you, it would be advisable to ask her in advance. If she approves, then go ahead and add her, however, there are 2 things you should keep in mind. First, since she's at a higher position, you would want to limit the content she can see. Keep it at a professional level. Second, depending on how the relationship develops, fellow volunteers may view it as though you're sucking up to her and that could alter any relationships you have with them. As long as you can manage those 2 issues, I see no problem.