At this age, we will assume that your child has been exposed to some water play, likes a little adventure, and is not afraid to put her face in the water. Encouraging your child to "face up" into the shower may also take away the notion that it is somehow harmful to get water in our faces, ears, eyes or nose. Blowing bubbles with the mouth or even the nose in the clean bath water, or encouraging the shower water to fall directly onto the face may help take away any fear of water in the face.
Then it is time to "get down to business" Kids at this age are usually very interested in bodily functions, so they're fascinated at the idea that mucus which is allowed to stand inside their nose and sinuses "transforms" into nasty stuff that needs to be cleaned out. It may help to demonstrate your technique to reassure your child that this squirt into their nose will come back out.
Be gently firm about the necessity of this activity, turn it into a game. They can understand the idea of their nose and sinuses being like a cave. Inside, it is dark and warm, with moisture dripping off the walls. The moisture collects on the floor and hardens, forming "snot-rocks", or pools of "booger juice". If allowed to continue, this nasty stuff can clog up their cave. If they want the "air carriers" to be allowed through, they must wash out the nasty stuff and keep the passages clean of snot-rocks. Girls this age may like a game of a princess, pony or a benevolent being living in the back of a cave which needs to be kept clean for access to the world beyond. Kids this age have great imaginations. If allowed to make up their own story about their cave, and the reason they must sweep it clean with a water hose every day, you will find they are much more compliant, because the story almost becomes real for them. Positive reinforcement for such compliance works better than nagging about non-compliance. Take a deep breath, both of you will survive. The best medicine often makes good sense, just keep your nose clean.
Please consult your physician first when teaching a young child to wash. Always consult a physician before allowing a child to wash if the child is fully congested (blocked) on both sides; has blocked ears or an ear infection; has recurrent ear or sinus problems; is disabled; or has difficulty tolerating the wash.
Use 1/2 packet of Nasopure buffered salt in the 4 oz bottle. Fill with purified, distilled, or previously boiled water. Close cap and shake until salt dissolves.
Encourage child to hold bottle as directed, but don't squeeze the bottle for your child. Allow the child to wash on their own, gently squeezing a small amount of solution (approx. 1 tsp.) into each nostril.
Encourage the child to blow gently.
Note: Allow your child to watch you wash first, while they play with the bottle, getting accustomed to the feel of the spray.