trying一問

In this sentence, trying is a present participle. "trying on different outfits" is a phrase which gives more information of the subject - She . There is another example:

Elinor, starting back with a look of horror at the sight of him, obeyed the first impulse of her heart in turning instantly to quit the room. (Chapter 8 Page 296 Sense and Sensibility - JANE AUSTEN)

In this sentence, "starting back with a look of horror at the sight of him" is a phrase which describes the subject -Elinor . starting is a present participle.