Most children who don't wet the bed at night have the ability to hold it all night or else they get up and use the bathroom. So it makes sense that a child who is unable to hold it all night MUST be potty trained for nighttime. Following are instructions on what worked with my oldest when he was about this age...he was a heavy sleeper:
At bedtime, have her lay down in the dark with all bathroom and hallway lights off just as if it is the middle of the night. Ask her to pretend to be asleep and then think about how she feels when she needs to go during the day and pretend she is having that feeling while she is pretending to sleep. Ask her what she does when she feels the urge during the day and have her practice "waking up", going into the bathroom, pulling her pants/panties down, sitting on the potty, pretending to go and then dressing, flushing and getting back to bed. Have her do this visualization and practice routine 5-6 times in the evening at bedtime. Within a week or two she will probably be getting up in the middle of the night to go and most likely will not even recall doing it. My son, now 14 still "sleepwalks" to the bathroom to use the toilet in the middle of the night. I read about and tried this technique right before we tried the sheet alarm or putting him back in diapers...no pull ups at the time.
I hope it works as well for you. Good luck!