Definitely get some Feliway, perhaps the diffuser. It really helps chill kitties out when they are dealing with changes & stressors. Toys would be good, catnippy ones... Giving her a snuggly bed and a cat post with a view are great things too... enjoy your new girl!
My birthday is the day after Christmas, so I like to do up the whole season. I always have the biggest real tree that will fit in my apartment, decorated with white lights and a huge variety of carved wooden animals and mini disco balls (my party animal tree). Around the apartment I hang light garlands, stockings, window kissing balls, table top decorations with pine cones... Last year I made new matching wreaths in green and gold and red that I LOVE... I love decorating for Christmas!
Don't forget to dangle snowflakes from the ceiling. You can do big ones, but also littler ones with multiple flakes hanging at different lengths along your string. I really like fishing line for this, since it's practically invisible. In addition, at craft stores you can get window paint (specifically designed to be easily washed of glass) and paint the insides of your windows with faux snow drifts gathered along the bottom/sides.
Since you have mini trees, you could also wrap little boxes to put under the little trees.