"My colleague's body is amazing"

Don't focus on her body.

Instead, say something like this:

I am envious of my colleague's constitution.
I wish I had my colleague's metabolism.

Both of the following definitions come from Merriam-Webster.

Constitution:

2 a : the physical makeup of the individual especially with respect to the health, strength, and appearance of the body
// a hearty constitution

Metabolism:

b : the sum of the processes by which a particular substance is handled in the living body

Or, if you do focus on her body, don't make it sound as if you're talking about her appearance.

You could instead say something like this:

I wish my body handled adverse conditions as well as my colleague's does.

Or simply:

I wish I had my colleague's health.

You are right that the word "body" in the first sentence might send the wrong message.

The simplest way to fix that is just say "My colleague is amazing". The following sentences then describe what is amazing about her.

In the last sentence, we already know why you think her body is amazing, so it will not be misunderstood, but you could change it to "Her metabolism is so amazing I'm envious" if you want to avoid any reference to physical attractiveness.

There are some words that actually convey the meaning you intend. Here are some examples applied to this situation:

My colleague is remarkably resilient.

Resilient: Able to withstand or recover quickly from difficult conditions.

My colleague has an imperturbable disposition.

Imperturbable: Incapable of being upset, unflappable

Disposition: Physical inclination or tendency

My colleague is indefatigable.

Indefatigable: Literally, untiring. Figuratively, not affected, put off, or overwhelmed the way others might be.

I would find the other suggestions awkward to say due to their "sophistication" or formality.

Here are some (mostly) simpler ideas. Many don't fully convey the meaning but of course could be qualified further in the conversation.

I think my pick would be X is bulletproof.

X is bulletproof/impervious/indestructible/invulnerable/invincible.

X is capable of withstanding anything.

Everything seems to bounce off X.

X is tough.

X is seemingly unstoppable.

X is hardy/robust/resilient.

X has a lot of grit.

X is really fit.

X can go for miles/run a marathon [without breaking a sweat].

Physically, X can deal with anything.

More colloquial:

X is a tank.

X is a machine.

X can really take a beating/pummelling.

This is not one I've heard before, but if I heard it I would have a pretty good idea of what it meant:

X has flesh of iron.

Which reminds me of the Iron Man/Iron Woman contest (this would depend on whether it is well-known in your locality).

X is practically an Iron Man/Iron Woman.

Here is a more sophisticated one:

X would put Achilles to shame.