I draw on a career of almost 30 yrs as an artist and art teacher. I am an award winning published fine artist by profession who also teaches and sells design packets to the Decorative art industry. The copyright laws that protect my intellectual property in the art business are the same laws that protect anyone in any industry that creates intellectual property - which is automatically protected at time of creation btw. Patents are not required to protect intellectual property from infringement.
I have more than a few friends who have spent years in court fighting infringement claims against companies that thought they could make and sell items with the artwork of the artist on it without permission - every time the big company lost. (think cute snowmen on gift items and a big national store) I have many times had studios teach my designs without permission and without even purchasing the patterns for each student in the class - each time I have found out about this I have confronted them and been compensated for my lost income.
Many times I have had painters submit a copy of one of my paintings to a juried art show representing it as their own work (yes they painted it but it is NOT their own work...it is a copy of my work)
For all of those reasons I went into limited retirement a few years ago and rarely teach or sell packets...although I have a class of 17 tomorrow that I should be preparing for. :-) I am a life long sewer and quilter who now has more time to enjoy my hobby....but I still do my own thing and rarely buy books or patterns.
"only the copyright holder has the legal right to derive income from their own intellectual property" is the accepted legal ruling.
If the copyright holder wishes to give permission to someone else to derive income from their pattern then they may do so if they wish - but you have to get specific permission outlining your intentions in writing for it to be valid...and to protect yourself!
The eventual selling the "one off" copy that you made from the pattern that you purchased is not the same as selling items from a pattern that you purchased for the intention of using to make items to sell - the intention or motivation for the intitial purchase is totally different.
In your experience, the copyright holder decided that you would be allowed to derive income from her pattern by selling items on Etsy...
...the next time you contact a designer - and please do so in writing not verbally for your own protection as a phone call is just a phone call- she may say no and you must respect her wishes, no way around it.
if in doubt always ask for permission! Ignorance is not the best defence in any situation. Creative people deserve every chance they can find to create income from their creativity - otherwise they may have to give it up and get a real job...and then there won't be any pretty patterns for anyone to enjoy.