Metro ladies t shirt cold shoulder adaptation

Hi, My fourteen year old announced to me that she would like me to make her a cold shoulder top to wear for a themed dinner at the end of the month. I have seen one put out by stylearc which looks to her liking. I really would like to use an existing tshirt pattern in my stash, namely the metro which is tried and trued where sewing for the teen is concerned. I am guessing that to make a cold shoulder adaptation I just take the cap off the sleeve. Is this right?? Do I take it off at the notches but add enough to hem? I can picture it and would play but the model is 500km away at school so there would only be myself or the toddler to try the attempt out on. Any suggestions as to the best way to go about it? Thanks in advance Tamara