Is it ok that my 13 y/o is getting her second dose of pfizer vaccine after 34 days of her first dose? is it still effective? is it possible to have less side effects? i totally forgot her appointment and we could only get appointment for that day?

Should be fine at 34 days. Get the second jab, and do not worry. Efficacy should be adequate, but cannot ever accurately predict potential side effects from a vaccine. Usually minimal and self-limited.

It's perfectly fine. The point is that you do not need to start over with dose #1. She will be adequately protected two weeks after the second dose. No need to worry.