Here's why:
* "Aunt studies" sounds like a phrase, not a complete thought. It needs a verb to make it a clause.
* "Compares prices from many" is also incomplete as a sentence. It lacks a subject.
Here's a possible correction:
My aunt studies and compares prices from many stores.
In this corrected sentence:
* Compound Subject: "My aunt"
* Compound Verb: "studies and compares"