that's a lovely idea!

i think a mug would be great (feels so much better to have your own).

if she's going to spending most of her time with you (rather than travelling) maybe a map or something? it's a pity we don't have A-Z's here - a small version of that is great to have when you arrive in london.

maybe her own set of keys? i know you can give them to her but it's kind of nice to have them as part of a welcome pack.