J.A.
For a very easy center piece you can buy a potted Ivy at the plant store. If it's in one of those ugly plastic starters, just buy a nicer pot that it fits in snugly. Now go to Albertson's, Costco, Ralph's (where ever) and buy a small bunch of roses and/or carnations. (Perhaps white and/or pink.) Cut the Rose very short at an angle and push them into the Ivy. Voila! Inexpensive, Long lasting, and Looks like one you'd have bought from a florist. The Ivy works as the florists base and the green of the arrangment. as the rose buds start to open, it almost looks like a topiary. (spelling?) In a 7" pot I used 9 roses, but could have done just 7.
Hope she enjoys all you do for her! Have fun, -J