I don't want this manifestation to happen...

Dreams cannot really be interpreted quite as literally as you are suggesting. If you have a dream involving a particular scenario then it doesn't mean that particular scenario is now on the verge of physically happening.

All it means is that the subjects you chose to become involved in the dream are able to express the feeling contained within the dream. You created every part of the dream yourself.

For some background to the rest of this answer, you'll need to read and understand: Something in my dream made me believe I could bring a dream item back to the ‘real’ world. Am I going crazy?

From what you've said in this question and some other recent questions of yours, it sounds like you are predominantly experiencing feelings of "helplessness" in your life at the moment. That's not a bad thing or a good thing, it's just a thing.

(I realize that "Helplessness" may not be an accurate word to describe what you're actually feeling but let's just use it for the sake of this explanation)

Since you create every aspect of dream reality (just like you create every aspect of physical reality), the characters you choose to play out the dream just represent the feeling. The dream reality mirrors the feeling just like physical reality does. See the example of mirrored "frustration" here.

For example, let's say your neighbor has a cat and you don't really like cats (or animals in general) and you especially don't like that one. Now if you had a dream where you watched that neighbor's cat get run over by a car, you might have a fairly minimal negative emotional reaction to the event...it probably wouldn't be a vibrational match to a feeling of "helplessness". So you wouldn't use those dream characters to express the feeling of the dream.

So in order to express this vibrational attitude of helplessness within your dream reality to yourself, you instead use the dream-created character of a loved one, who it sounds like you do deeply care about, and you create a scenario where you cannot help them. That sounds like a much better way of "playing out" the feeling of helplessness.

The scenario of the dream is a perfect vibrational match to your current dominant vibrational attitude

It doesn't mean for a moment that the scenario will play out physically but it is an example of where the current vibrational attitude is leading towards. The dream is acting as a leading indicator of what kinds of vibrational matches you can expect in your physical reality if you continue with this attitude.

But it's not something to fear - it's just an indicator.

For example, if you are driving in your car over the speed limit in an area where there are plenty of traffic cops with radar speed guns then your speedometer is indicating that the present speed is probably going to land you with a speeding ticket :)

The speedometer is nothing to fear, it's just an indicator...it's providing you with useful information.

In exactly the same way, the manifestations in our physical realities are useful indicators of our vibrational attitudes. And exactly the same thing applies to the manifestations in our dream realities ("dreams").

So a dream like this that generates a strong emotional reaction within you is providing valuable information for you.

The dream is effectively telling you: "Hey Buddy, in case you've not realized it yet, there seems to be a predominant attitude of helplessness permeating your life right now. Just thought you might like to know, that's all. Bye!"

So what do you do with this valuable information?

Assuming you don't want your physical reality to end up with vibrational matches to the dream feeling, you could simply apply some methods or techniques to find ways to feel less helpless in how you currently feel.

Or, if you want a less "head-on" approach, you could just find ways to feel better/good in your life right now and that will naturally take your attention off any negative feeling attitudes you might have habituated towards recently.

But if you're now thinking that there's a lot of hard work involved in going from a strong negative feeling to a strong positive one, you can relax because it's not that way at all.

It's actually much easier to go from a strong negative feeling to strong positive feelings because you've already built up a large amount of energy that is ready to be released...just like releasing a stretched elastic band.

The slightest bit of ease you introduce into your vibrational attitude will send you shooting towards some joyous feelings instead.

There is more about this idea in: How to increase density of desire for some thing to manifest it easily ?

Hope that sheds some light on this subject for you.