How does the Silence train / raise this person?

Question

The silence kidnaps

Melody with the aim of raising her as a weapon against the Doctor.

But they dont exactly train them for anything do they? Nor do they make them hate the Doctor by any brainwashing sci fi technique to convince them to kill the Doctor.

The one way they do use them is by

putting her in a suit that controls her physical movements/actions.

If that was their ultimate method, what was the point of using them at all. Any person in a weapon suit can try to do that.

Answer 1

She has been brainwashed

From "Let's Kill Hitler" (S06E08):

MELODY: Well, now, enough of all that! (pulls a gun and aims It at the DOCTOR) Down to business.

DOCTOR: Oh, hello. I thought we were getting married.

MELODY: (walks towards them) I told you, I'm not a wedding person.

RORY: Doctor, what's she doing?

DOCTOR: What she's programmed to.

RORY: Where'd she get the gun?

DOCTOR: Hello, Benjamin.

She was raised by the Silence, whose specialty was brainwashing people (that's how that got humanity to go to space, and ultimately the cause of their downfall). Besides being brainwashed, she was also raised to believe that the Doctor deserved to be killed for failing humanity.

From the same episode:

TEACHER: Mels?

MELS: A significant factor in Hitler's rise to power was the fact that the Doctor didn't stop him.

Why did they put her in a suit?

That wasn't necessarily their only plan. They wanted a part-Time Lady assassin, who would have the skills necessary to take down the Doctor. Indeed, River previously tried to kill the Doctor with poison (and was very nearly successful at it). She might have benefited from her skills as a Time Lady (for example, regeneration) in doing so. The suit may have been a backup, in case she wasn't able to kill the Doctor of her own volition.

It's pretty unclear why they couldn't simply have put someone else in a suit in that case. Maybe the suit was only compatible with Time Lord physiology. Or perhaps it was because "destiny says so," and River simply had to be the one to (apparently) kill the Doctor, one way or the other.

Answer 2

Well, we aren't shown a lot of the time that the character in question is held by the Silence.

However, in Let's Kill Hitler, we see that the character has a very clear compulsion - which was probably instilled during the time they spent with the Silence.

As for the suit:

The suit does seem to be part of the conditioning - but we do see River want to kill the doctor without the suit. The suit is used again later to reinforce the compulsion after it is seemingly broken. Although it still is not strong enough...