We see this every year. If you don't want them in there then open the gate, but in my experience momma had her in there because it was safe.
We have them every year, up to 4 one year in about a 1/3 acre back yard. The does come in and drop fawns then leave them there and go eat and come back a few times a day to check on them. It will amaze you how fast they will be able to jump a 4' CL fence if they are pressured. It kinda stinks because we loose the use of the yard for a good bit during the spring, but its cool to watch too. Only have one so far this year.