Etiam dominam iustam esse decet.

The core pattern is:

• decet = it is fitting / it is proper / it befits
• a person in the accusative
• plus an infinitive phrase

So here:

• dominam = the person concerned
• iustam esse = to be just

Very literally, the sentence means something like:

• It befits even a lady/mistress to be just
• or It is proper for even a lady/mistress to be just

Because iustam agrees with dominam.

• dominam is accusative singular feminine
• iustam is also accusative singular feminine

Latin adjectives must match the nouns they describe in:

• gender
• number
• case

So if the sentence has dominam, the adjective describing her must also be iustam, not iusta.

Because after decet, Latin normally uses the infinitive to express what is fitting.

• esse = to be
• est = is

So:

• iustam esse = to be just
• not she is just, but for her to be just

That is why the sentence is not making a plain statement of fact. It is saying what is proper.

decet comes from decet, decere, meaning:

• it is fitting
• it is proper
• it befits

It often has a nuance of appropriateness or suitability, not just bare obligation.

So dominam iustam esse decet is a little softer and more elegant than a blunt must statement. It means something like:

• A lady ought to be just
• It is proper for a lady to be just

Not in the ordinary nominative-subject sense.

A native English speaker often expects the person doing or being something to be the subject, but Latin does not build this sentence that way.

Here:

• decet is the main verb
• dominam is in the accusative
• iustam esse is the infinitive idea

A useful learner-friendly way to understand it is:

• dominam is the person for whom something is fitting
• iustam esse is the thing that is fitting

So dominam is not a nominative subject like domina would be.

Because Latin often uses an accusative + infinitive type of structure.

In dominam iustam esse, the idea is:

• the lady/mistress = the person being described
• to be just = what is said about her

So although dominam is accusative, it is still the person understood with esse.

You can think of it as:

• for the lady to be just

That is why iustam agrees with dominam.

etiam usually means also, even, or still, depending on context.

In this sentence, because it stands before dominam, it most naturally emphasizes that word:

• even a lady/mistress
• or also a lady/mistress

If the meaning already shown to you uses even, that is very likely the intended nuance here.

So Etiam dominam... decet often feels like:

• Even a lady ought to be just

Because it is the normal third person singular form of the verb.

With this kind of construction, Latin commonly keeps decet in the singular:

• te hoc facere decet = it is proper for you to do this
• dominam iustam esse decet = it is proper for the lady to be just

English may want a clearer personal subject, but Latin is happy with this singular verb.

They do not mean the same thing.

• domina iusta est = the lady is just
  • a plain statement of fact
• dominam iustam esse decet = it is proper for the lady to be just
  • a statement about what is fitting or appropriate

So the Latin sentence is not simply describing her. It is expressing a judgment about what she ought to be.

Yes, Latin word order is much freer than English word order.

This order gives a natural emphasis:

• Etiam first, highlighting even/also
• decet at the end, which is very common in Latin

Because the endings show the grammatical roles, Latin does not need a rigid English-style order.

So this sentence puts the pieces in an order that sounds good and emphasizes the idea well, especially etiam dominam.

Latin has no articles.

So dominam by itself can mean:

• a lady
• the lady
• sometimes simply lady in a more general sense

The context tells you which English article makes best sense. That is why translations may differ slightly even when the Latin is the same.

Yes. That is a very natural translation.

Just remember that decet is not exactly the same as a hard command like must. Its flavor is more:

• it is proper
• it is fitting
• it befits

So Even a lady ought to be just is good English, as long as you keep in mind that the Latin expresses propriety more than strict necessity.