There are a few things that could be improved.
For example, the PP "of her niece" modifies "portrait" and thus the NP object of "painted" in full is "a very big portrait of her niece".

Student or Learner
Hi everyone
Please kindly help to check my tree diagram and correct me if it's wrong
Thank you in advanced
https://www.picz.in.th/image/bXgDA1
ps. sorry, I don't know how to upload the photo TT_TT
There are a few things that could be improved.
For example, the PP "of her niece" modifies "portrait" and thus the NP object of "painted" in full is "a very big portrait of her niece".
Welcome to the forum.
Please note my corrections above. You must end every sentence with one appropriate punctuation mark.
In future, there is no need for a greeting at the beginning, nor to thank us in advance. Thank us after we help you, by clicking on the "Thank" button.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.