Well if you create a new disk on another datastore, it will appear as a new disk in Windows as well. (Unless you want a complicated life with Windows storage spaces spanning disks on multiple datastores) << This is not an option, merely sarcasm :smileywink:.
Your datastore is full so you need to tend to that issue anyway, you can't leave it like that.
An option would be to create a new Lun / Datastore, migrate the VM to this datastore and then extend the virtual disk / LV.