First, is it possible that someone else is waking up and bringing her into the bed with you? Does she wake during the night to eat? Is she bottle fed or breast feeding? If she is waking nightly, you are probably so tired, and automatically responding to her voice, picking her up, and bringing her in your bed so that you can sleep. This is not very unusual. Parents become so in tune to their child's voice that they respond automatically without thinking sometime. Is she walking yet?
I do not think that you are losing memory. Many mothers automatically respond to their child's call to them, automatically. You are probably in your deepest part of sleep when she fusses and you go get her to comfort her and put her in your bed and continue sleeping. Is her bottle in your bed when you wake up? If you are able to establish the time that she wakes each night, then you can set your alarm just prior to that time, so you will train yourself to get up. She must be a very good girl, since she sleeps quietly beside you and doesn't wake you up. Children love that closeness and it has probably become a habit by now. If she was walking and was going around the house while you slept, I would be concerned. I think you are very tired, as new mothers can be. Make sure you are eating a good healthy diet and drinking water. I would not be worried about this, especially if your energy level is good during your wakeful hours, however you can discuss with your doctor or the pediatrician to get some their thoughts.
Enjoy your little one!