Interpreting 本人がどうにかするしかないことなので

Question

I just started reading a comic, and I'm having a bit of trouble understand a line said in the first page. Basically a girl approaches her guy friend and tells him that she's been worried for him since he hasn't been in school for 10 days, the guy responds by saying he was sleeping. She then says

はいまあ、ゆっくり見守ってやるつもりでいます。本人がどうにかするしかないことなので,

The guy then responds with まあじ?

I'm a little bit confused on what is trying to be said in the latter part of the sentence. Is she saying she has no choice but to look over him in person because he's been skipping school?

Well, my intentions were to keep an eye on you, looks like I have no choice but to do in person

Answer 1

I think you're confusing who 本人 is referring to. Looking at the context, the speaker is probably talking about a third party rather than the listener. I think we should break the sentence down a little more. It looks like you understand the first sentence, so:

はいまあ、ゆっくり見守ってやるつもりでいます。
Yeah, well, I intend to just watch over (that person).

Although this sentence doesn't say who they are watching over, it implies that there is someone that they are watching over. So that person is who 本人(the person themself) is referring to. So,

Word/Phrase	Meaning
本人が	The person him/herself + subject marker
どうにか	Somehow / Some way or another
する	Do
しかない	Have no choice
こと	nominalizer
なので	"So". Shows cause and result

So if you string the first three together, you get:

本人がどうにかする。
The person does something about it themself.

Adding the next「しかない」, meaning "having no choice" after a verb, you get:

本人がどうにかするしかない。
Have no choice but to do something about it themself.

Adding こと nominalizes the phrase:

本人がどうにかするしかないこと。
Something that the person has no choice but to do something about it themself.

And then finally adding なので just gives you a hanging "so..."

本人がどうにかするしかないことなので、
It's something that the person has to something about it themself, so...

Maybe that's not the most natural translation, but I hope you get the gist of it. This second sentence explains the reason why they are just watching over the person in question. You could probably flip the two sentences over and get:

本人がどうにかするしかないことなので、ゆっくり見守ってやるつもりでいます。
(It's something) the person has to do something about it themselves, so I intend to just watch over them.

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^{also I really just wanted to use the tables cause they looked cool}