THIS IS A CHALLENGE!
The curse still happened and everybody was still sent to Storybrook. Emma still grew up in our realm and had Henry at 18. Regina still adopted Henry. Emma is still the daughter of the Charmings.
At age 20, Emma was killed. The moon brought Emma back as the winter spirit.
The moon sees everything in any realm. The moon has plans for Emma.
(Emma can transition between a spirit body and a physical body...but still dead. Like a Whitelighter from Charmed)
In the Enchanted Forest, the seasonal spirits are worshipped for the bringing of the seasons. But no one has seen them till now.
When Regina and Emma meet, it's when Emma tries to throw a snowball at Regina to make her smile.
Surprise surprise! Regina can see her. Regina can see her because Rumple once told her the story about the Moon and its spirit guardian's and she believes it. Henry can see her too because he is the truest believer. Rumple can also see her and is doing his plotting thing.
Regina and Emma grow close and start a relationship but it's hard to have a relationship when only a few people can see you. That is until the curse brakes. Not to mention Emma still has to do her job and bring winter when the time comes.
Plus when magic is back in Storybrook and Emma and Regina get it on, well magic happens and now something never before seen is happening. A spirit baby is growing inside Regina!