J.S.
Hi D.-
Party America off of Cajalco in the Crossings center turned into Party City and they have great prices. All the tableware is 1/2 off. I get a lot of things there. If you are making her cake there is a cake supply shop In Norco. Heading from Corona inot Norco it is on Hamner before Second. Sorry I can't remember the name-the buildings are an orange/yellow stucco color. I think they also have favors.
Parks-
Yorba Regional Park in Yorba Linda is fantastic (off the 91 at Weir Canyon). You can get there in 20 minutes with no traffic. This is one of our favorite parks and worth the drive. You can rent little paddle boats for the lake and feed ducks. Great for a picnic. In Riverside, you can try Fairmount Park (near downtown) or Cirtus Historic Park (off Van Buren). I think they both have lakes. Prado park is off the 71, technically in Chino but very close to Corona.
Hope these help you out.
J.
For a park here in town, Citrus Park on Rimpau and Santana (near the Walmart on Ontario) is opening a new water playground August 19. We were there over the weekend and it looks like fun.