Im a midwife and lactation educator in Richmond.
I can tell you that she associates mama with breastfeeding. If you want to be able to be away from her for a little longer, try her with whom ever her care provider will be with the bottle or cup. You will have to not be in the room at all, or she will likely not accept the breast substitute. Try leaving her in the care of her sitter/other parent, and go to another room of the house, say to work or whatever, and see how she reacts to taking the breast substitute from the care provider. She may balk at it the first couple of times. Try it when you know she will be hungry, so that she is willing to put forth the effort to get the food into her belly.
At 4 months nipple confusion is unlikely, but I suppose still a possibility, so be aware that this situation could occur. Also... Stopping nursing exclusively may interfere with your milk supply and your fertility. If you havnt gotten your cycles back, skipping nursings will likely cause them to start up again. Be sure you are emptying your breasts often, try not to go longer than 6 hours without nursing, as it could cause you to drop your supply and/or get a breast infection. Your body will tell you when you MUST get that milk out, listen to it.
Are you involved with La Lache League? They are a wonderful organization for helping and supporting breastfeeding moms and there are morning and evening groups around Richmond and Williamsburg.