There are problems with the claims.

In summary: someone that in Sweden acts to defend themselves while "in peril" when subjected to — or are in imminent risk of — a criminal attack, will not the convicted, unless the act is "blatantly unjustifiable".

Context, and how to just what a fictional character is saying

We have a problem here in Sweden with people being ill-informed about the right to self-defence, and this is compounded by people with opinions spreading myths about it. Often these myths err on the side of claiming you have less rights than you really have.

So, two things before we go on...

1. The characters may have been unreliable. Do not ever assume that just because a character says something in a work of fiction, that the character is meant to know what they are talking about.

And even if they are meant to know what they are talking about...

2. The author may have been unreliable, and done their homework poorly.

Keep this in mind...

That said, the right to self-defence is not infinite.

The law

According to the Swedish Criminal Code (Brottsbalk, 1962:700), Chapter 3, §§ 1-2 and 6...

• If you intentionally kill someone, you get convicted of "murder"
• If you intentionally kill someone, but there were mitigating circumstances, you get convicted of "manslaughter"
• If you act in reckless disregard for the risk your actions are causing, and this leads to the death of someone, you get convicted of "causing the death of another", or what we here can call "reckless killing"

And Swedish Criminal Code (Brottsbalk, 1962:700), Chapter 24, § 1 states that an act performed in "peril" shall only lead to a conviction if the act was "blatantly unjustifiable".

"Peril" is enumerated to exist in cases of...

• A commenced or imminent criminal attack on person or property
• A person has gained or trying to gain access to a room, house, yard or ship
• A person that refuses to leave a domicile after being told to

When judging whether an act is "blatantly unjustifiable", the prosecutor must look at...

• the nature of the attack that caused the peril
• the significance of that which the attack was aimed at (such as a human life)
• Other significant circumstances

That last bit is interesting because it takes human psychology into consideration, and let the defendant's assessment of the peril be the standard by which the act is judged.

The claim

Let us start with the easy bit first...

"if she killed the intruder, under Swedish law, she could very well be charged with manslaughter, and possibly murder if it could be proved that she placed the golf clubs around the house ahead of time."

Murder? No. According to the Swedish Criminal Code (Brottsbalk, 1962:700), Chapter 3, §§ 1-2, a person that kills an intruder in their home could at the most be charged with manslaughter, because there are mitigating circumstances, i.e. the person felt threatened and there was a home invasion in progress.

In order for this to become murder, she would more or less have to have invited the assailant or in any other way drawn them in with the intent to kill them.

Yes, she prepared to defend herself or a potential intrusion, but without knowing for certain that the assailant would come at certain time or at least a certain day, any kind of premeditation towards killing is more or less impossible to prove.

With this, murder is off the table. That claim is simply wrong. Whether it is the author or the character that is erring, I cannot say.

So, manslaughter then, or the even lesser degree, called "causing the death of another", or reckless killing.

Manslaughter would come up of she — when whacking them with the club — did so with the intent of killing them.

The operative word here being intent. The prosecutor has to prove that intent.

Sure, we can dream up scenarios where this is the case; the classic reason for why people do get convicted even acting in peril is when they keep harming the assailant after the danger has passed.

But — again — just preparing for a potential intrusion is not enough to prove that intent.

Finally, reckless killing. This is where such cases usually ends up. And — again — this usually happens because the defendant did something when the danger has obviously passed; the criminal attack was no longer imminent but passed.

Conclusion

Unless the protagonist in question had set up lethal traps; unless they had foreknowledge of an attack; unless they invited the assailant in with the intent to kill them; unless they fend off the attack and gets themselves into a perfectly safe situation and then proceeds to beat the assailant to death, then it cannot become murder.

Manslaughter or reckless killing, yes, there will be an investigation for that, but from the description of the situation — the protagonist fearing the assailant is dangerous and means them harm — preparing a home defence with strategically placed golf clubs does not in any way preclude the prosecution being dismissed as justifiable self-defence.

Only(!) if the protagonist keeps harming the assailant after the home invasion has been staved off / neutralised, can a conviction for manslaughter or reckless killing become a possibility.

Summary

Yes, in Sweden a prosecutor will look at the case when you kill someone.

But — no — in the situation described, a home invasion by someone perceived as wanting to cause harm, this is very unlikely to become "murder", for lack of premeditation.

The remaining possible charges — manslaughter or reckless killing — will only result in a conviction if the situation was obviously and provably harmless in the eyes of the defendant, and they still killed the assailant.