That is a matter of opinion, some say over night, others a couple of hours. Personally its not something that has ever worked for me. I have heard of it working very well for lots of people but every time I have tried, no dice! So dont be too worried if she doesnt take it, if she does yay!
How often are you trying to feed her? Offering prey items too often can put a snake off of food for even longer, offer every 5-7 days and you should be safe.
When are you offering food? Night time is when they are most active and most likely to accept a meal.
How are you offering the food? A snake will react better to a hot/warm mouse then a cold one. Try dangling the mouse close to the snake (but dont force it out of hiding, leave her be), if nothing happens leave the mouse at the entrance of the snakes hiding place over night, toss out the mouse if it is still there in the morning.
Also, this is the hard part, dont start to hold the snake again until it starts eating! Holding the snake as often as you were before it was acclimated properly is probably what has put her off food. It is the main mistake I see novice keepers make right along with heating but it sounds like you will have that figured out soon
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Once she starts eating take is slow, hold once a week for a couple of weeks, then twice, so on so forth but never hold the day of or the day after a feeding until she has grown some.
Scenting the mice has worked well for me in the past. I have dipped the mouse in tuna water with great success starting troublesome hatchlings, where that failed usually rat scent would prevail.
Hope this helps!