Hi There
If your j curl wont bond to your ladies natural lash then my guess would be that her short lashes could have more of a curl to them than the curl of your j curl extension. So take another look at her lashes and try to work out what would be the best type of curl extension-wise to use on her, she may need a b curl which is slightly more curlier than a j curl. Have a look back through your lash extension manual it should all be in there!!!!!! If not ask your training provider as this information should be included on your lash course. Have another look at all the various styles of curls there are in lash extensions and how they all bond differently to different types of natural lash and the answer should come to you. If you dont have or cant get this information let me know.
Hope that helps, Lee-Anne x