The manager, along with her assistants, _______ the company retreat.

Along with someone/something (phrase): 
English Meaning - In addition to someone or something else. 
Bangla Meaning - সংলগ্ন হওয়া। 

• with, together with, as well as, along with, in addition to, accompanied by দ্বারা কোন noun বা pronoun যুক্ত হলে এদের পূর্ববর্তী subject অনুযায়ী verb হয়।
Examples: 
- The principal along with the teachers was present in the meeting yesterday.
- Mr. Amin accompanied by his colleagues was present at the party.

Complete Sentence - The manager, along with her assistants, is organizing the company retreat.