My wife had a forcep delivery 2 months ago. From then, my daughter had a problem with her right hand. She is not able to pick her hand upwards. How?

Palsy. After the head is delivered during labor, the dr must tug on the head to get a shoulder to emerge & that tug can stretch the nerves that exit the neck & supply the shoulder, arm & hand on that side. This can cause a swelling in the nerve & loss of function until the swelling goes down. "erb's or klumpke"s palsy" are lables used for variations.If not resolved by now seek therapy for baby.
Nerve damage. Is possible, was the baby fine at birth or was the arm weak then? Normally a rough delivery and shoulder dystocia are noted at birth, and most kiddos regain movement quickly.
Brachial palsy. It seems your infant has not been making a noticeable progress. It would be appropriate to have your baby evaluated by pediatric neurosurgeon.