It is extremely difficult for most autograph collectors to get autographs from the hottest names in Hollywood. Even if a collector spots a star they still have to deal with a crowd of fans, the celebrities security, and even the celebrity herself may not want to give autographs at that time.
Consequently, most of us end up buying them, which is fine but can be expensive and, unless you get both a Certificate of Authenticity and a Money Back Guarantee, then you can't be positive that what your buying is authentic.
However, there is another option. You can write an autograph request. While it is not guaranteed you will get an autograph back, it only costs you the price of a postage stamp.
Each actress is different but it is surprising how easy it is to get autographs from some of the hottest stars in Hollywood when you know how.