The egg laying process is pretty complicated. A lot of things have to go right for them to lay a perfect egg. Many pullets get something wrong when they first start laying but most of them straighten things out fairly soon. Don't totally give up hope yet but I agree, don't absolutely count on her straightening it out. 14 weeks is very young. Her age worries me more than anything else.
A pullet or hen should only release one yolk a day. There are different trigger mechanisms that tell her to release one to start the egg making process. The eggs should be laid during the day and it takes about 25 hours for the egg from releasing the yolk until the egg is laid. This can vary from hen to hen but 25 hours is a decent average. So one trigger to release a yolk is daylight. If a hen lays eggs on consecutive days another trigger is laying the egg to get the next one started. Since they want to lay an egg during the day instead of at night, late in the day is a trigger to not release an egg until the following morning.
Sometimes a hen messes up and releases two or more yolks at the same time. That can give you double or triple yolk eggs. If they are released at separate times you can get two or more eggs in one day. They share room in the shell gland so you can often see marks where they were touching in the shell gland.
A hen typically makes a limited amount of shell material each day, enough for one egg. If she lays two the same day the second egg is often thin-shelled or shell-less, like yours.
Most of my pullets get the egg laying thing correct from the start. The ones that don't (laying weird eggs, laying from the roost, etc.) tend to correct within a few days. The conventional wisdom on this forum (whatever that is worth) is to give her two weeks to straighten up before you get too excited about it.
I wish you good luck!