You just answered your own question. It's the 4th of July; so make it easy on yourself. If you want, add some stuffed animals for your baby in the mix. There will be plenty at Walmart and Walgreens; maybe even target. ( they are usually blinged out with red, white, and blue on them.
Or, just pick something that she likes and add a little red, white, and blue in the mix.
At 1 yr, my husband and I did a pirate theme as this is what we like and my son's room is nautical/pirate. His birthday is July 10th, and this year we're doing a motorcycle theme. At 1 yr, it really didn't matter and this year it doesn't either but he is a little older.
He likes Elmo too, so I am going to add Elmo to his cake. I did look for Elmo items but didn't find too much when I was out. I could have ordered them online; however, he loves motorcycles too. Maybe he likes them because my hubby has one and he sees them all the time. We are surprising him with this theme as he gets so excited every time he sees them.