Translation:She strongly resembles her grandmother.
Ressembler is just one of those french verbs that need à after them and before the indirect object in the sentence. The english equivalents don't always have a preposition. Obeir is another one.
Les enfants n'obéissent pas à leurs parents - The children don't obey their parents The preposition à is needed before the indirect object. NB No preposition for a in the English translation.
Other french verbs needs à after the when they are follwed by an infinitiveHave you come across continuer à marcher yet? If not - you soon will : )
http://www.frenchtoday.com/blog/why-french-verbs-followed-preposition-a-infinitive (This is the easy-to-read blog of a "learn to speak french" site. There is heaps of useful and interesting info on the blog pages. Use the search box on the site and key in "blogs" Blog titles will appear with blue tabs indicating what they are about (ie whether just general interest or tips with french etc)
http://french.about.com/od/grammar/a/preposition_a.htm (This one has three pages on the use of à)