Danielle looks exactly like...
JUDY GARLAND.
Particularly her eyes, most of all, and how they're set widely apart; her nose, her mouth, and the shape of her face: all very similar, practically identical.
Compare:
Judy http://www.wildsound.ca/images/judy_garland_black_and_white.jpg
Danielle http://vignette2.wikia.nocookie.net/theflash/images/e/e5/Caitlin_Snow_Danielle_Panabaker-3.jpg/revision/latest?cb=20141120033044
Judy http://www.doctormacro.com/Images/Garland,%20Judy/Annex/NRFPT/Annex%20-%20Garland,%20Judy_NRFPT_13.jpg
Danielle http://vignette1.wikia.nocookie.net/theflash/images/2/2f/Caitlin_Snow_Danielle_Panabaker-9.jpg/revision/latest?cb=20151029063431
Judy https://upload.wikimedia.org/wikipedia/commons/8/84/Judy_Garland_in_Meet_Me_in_St_Louis_trailer_2.jpg
Danielle https://pbs.twimg.com/profile_images/655024434663804928/vZ4-yydc.jpg
Judy http://www.milosctopasja.com/public/JUDY.jpg
Danielle http://www2.pictures.zimbio.com/mp/SUeDsE8KTy-x.jpg
I get so amused by the other threads here debating who she looks like, because when I see her on screen in The Flash all I can think is the second coming of Judy Garland, so obviously Judy Garland's Doppelgänger. It's most apparent when you forget about Judy's Wizard of Oz look, and compare 1940s pictures of her in her 20s, around the same age Danielle is now. Any slight differences between them are superficial, from the 1940s-style makeup and hairstyling vs. the 2010s.