There are two issues here.
The first is that the OP says that she has never spent a night away from her DD. Thing is, regardless of what access arrangement they reach the OP is going to have to learn to spend nights away from her dd, most likely a night a week and every other weekend.
The second is whether 50/50 really is in the interests of the child, and tbh I think that it depends very much on the child and the circumstances. For some children it works, for others it doesn’t. When me and eXH first split we agreed 50/50 on the basis I had no intentions of ever withholding access to ds. DS would spend two nights a week and every other weekend at his dad’s, and even he said that he was glad we had done it that way.
However, as I wasn’t working at the time (I had given up work to bring up DS and had then started looking before we split) I would still pick up DS from school or he would come to me once he was going to/from school on his own, so I did still see him most days and then either eXH would pick him up on his way home from work or he would go there himself as he got older.
However, after eXH’s partner moved in DS was no longer comfortable going there for various reasons and the time he spent there gradually reduced to the point that he stopped staying there altogether around two years ago. But he’s a teenager now so it’s about what he wants rather than what the parents demand, iyswim.
EXH did want to do one week on and one week off but I put my foot down over that as I knew that DS would never want that,and he didn’t even when it was suggested.
But I do think that as the OP’s dd is so young the arrangement could work to start with and then change as she gets older. But don’t count on it iyswim. As teenagers mature they often do need a home base,but again it’s a very individual thing and depends from child to child.