The word should be beautiful.
Beautifully is an adverb which describes a verb. Beautiful is an adjective which describes a noun.
In your example, you're describing the "actress", a noun, so beautiful is the one to use.
You're not describing the verb "looking" or the act of looking, so the adverb is not used.
English Grammar - Word Endings - What are suffixes?
http://www.engvid.com/ Do you always know which words are verbs, nouns, adjectives, or adverbs? If not, this grammar lesson on suffixes, or word endings, will ...