Carrying a pillion is a whole new ball game, has the pillion ever ridden pillion before? I know it may be a strange question to ask, but unless they know what they are doing nasty things can happen. They have to learn to lean, they need to go with the bike & to fight the natural instinct to stay upright. The bike will change direction if they move about on the seat, or they lean to look at something especially with a light weight sit-up & beg like you have. The first few corners will be interesting for you, but Jane's a sensible girl, I'm sure she'll soon realise the score, but if you're going to do a lot of 2 up stuff, then get ready with the For Sale sign, you haven't enough power for serious distances. Also be aware that her knees are our wider than yours, so no cutting in, your acceleration will be down by 50% so you will have to plan overtakes not just simple go for them.
Last one, the pillion ALWAYS comes off worst in an accident, so be careful with her, Jane that is, not the bike.
Alan...