NoD said what i was thinking ^^
Every artist is different . Some work much faster than others (and some work faster or slower depending on what life throws at them *is thinking of myself and my own artwork*
. The main problem with your situation is that even if you'd agreed a time with your customizer, things went wrong for them IRL and now they have stopped with the communication and not been active here either....
I guess what you need to do is to have a think about if you still want to go ahead with this trade (if its still possible). And of course you'll need to talk to the person. Do you have their email addy? know them on facebook? if not perhaps you can do a "Looking for ....(insert persons name) thread here so that close friends who may still be in contact with the person can help you reach her. Then you can try sending the person an "Urgent response needed " PM /email .
Since things didnt go to plan with the trade , you can let the person know that you feel that its best to cancel the trade considering the circumstances - if the person had not already made your customs- and if thats what you want to do. It might help ease some of the pressure off her as well if she is still dealing with difficulties IRL and she hasnt been able to work on your customs . If you (and the person) still want to carry on with the trade then you'll both need to discuss a new timeline. You probably dont need me to tell you this but dont send the pony until this is all worked out and your customs are ready- dont send it in advance- especially if communication has stopped or is spotty