J.M.
I wouldn't worry about it too much. We also had my daughter's 3rd birthday at home. We had more kids (10 or so) and basically they just played together with her toys. Don't schedule too much, because (assuming a 2 hour party) about an hour of it will be spent snacking and eating cake and getting in and out the door.
We did have a small scavenger hunt that went really well. I went to iparty and bought a ton of small rubber ducks and hid them all over where the kids would be in the house. Each kid got a bag with their name and they went hunting. Then they got to keep the ducks they found. It was fun. It did go really fast though. Another option is freezedance. Very popular with the 3 year old set, doesn't require any set-up or clean-up, and can go as long as the kids are having fun.
But again, they basically just want to play together. I recommend warning your daughter a lot that when her friends come over they are all going to want to play with her toys (I don't know how she is about sharing). That way she doesn't melt down that other people are touching her stuff and she can have a good time.
Have fun!