You should look towards your child becoming dry at night when she is reliably dry during the day. Most children are daytime toilet trained by the time they are three years old.
It is not at all unusual for a four-year-old to still be in night-time nappies and even then, many continue to have the odd accident throughout childhood. Girls tend to be dry at night sooner than boys.
If your child has a saturated nappy in the morning (and is no longer taking a night bottle) this is a sign that she is not yet producing enough of a special hormone called vasopressin. This hormone inhibits urine production at night and until its action kicks in, your child is not yet ready for night-time training.
You can help your child to develop healthy bladder control by offering her plenty of fluids during the day and dropping feeds or big drinks during the night.
Once your child is confident with using the potty or toilet during the day and has dry(ish) nappies fairly consistently in the morning, you can take this as a signal that it is time to start night-time toilet training.
As with so many milestones, helping your child to become dry at night is more effective if you follow her lead. If possible, it is best to wait until she expresses a wish to try to sleep without a nappy or pull-up and then keep the whole process as relaxed as possible.