Would you consider Melania Trump to be "fit?"

I'm guessing you mean physically fit and not fit as in equipped to be flotus.

If she sneezes you will see even more how fit she is, since most of her fitness is on display.    I think you need to have back muscles of steel to hold those things up.

Certainly.  Both physically and mentally.

They seem to be a nice person.

They should be nice to they in only my personal opinion.

Since you did not qualify what this "fit" is you are referring to...I will take license to say she is not only fit in terms of being in incredible shape, but she seems well schooled/educated, elegant, passionate discourse to speak to the various demands of her upcoming role as first lady. 

yep

I have no advice for her.  ;)

Physically I would say yes. I don't know about anything else.