I would do an ABC scavenger hunt. That will get the kids thinking of all the letters and what begins with that letter. You could even write out a whole list of things that they have to find that begins with that letter or let them get creative.
You could make a scrapbook for your daughter either before or after the party that has one page per letter and shows a photo of her with each letter. For example, I made a scrapbook for my son and each page has a photo of him during his first year that corresponds to each letter of the alphabet. For the letter 'D' there is a picture of him and his Daddy so it says Daddy on the bottom of the page below their picture and on the top it has the letter. I made it to help him learn the alphabet and thought he would be more interested in it if it had his photos in the book.
A game idea could be if you printed out a list of the alphabet and then each child has to come up with something that begins with that letter and write it down. The parents could do the writing and the kids have to come up with the words that begin with each letter. You could even narrow it down so it has to be animals that begin with each letter.
You could do charades and write down something for each letter and then have the kids pull a slip out and act out that item. The parents could help / participate in that as well.
Make your own version of Outburst with the letters. For each letter write down 10 of the most common items that begin with that letter. Make it something the kids might think of. Then call out a letter and start the timer and the kids have to yell out things that begin with that letter. As the things are called off that are on your list, cross them off. You could even divide the kids into teams of 2 and randomly give each team a letter until the whole alphabet is used. The adults could even participate in this and it should be interesting to see what words everyone comes up with.
I am sure whatever you end up doing, your daughter will have a great time. I hope some of these ideas help. If you need more info on any of them, feel free to contact me.
-M.