I think probably to keep it boring a filler middlename would be best. Like
Ann,
Rose,
Marie,
Lynn, etc.
You could also go another route and choose a name that is just ugly -it really won't be boring because its so ugly but it could reflect how little her family cares.
Agnes comes to mind for this. Although, that's just my opinion - so if you like
Agnes I'm sorry!
BTW... I don't think
Jane is boring at all. Its classic. :)