היא תמיד מתנהגת בנימוס, אפילו כשהיא לא מסכימה.

Because the subject is היא (she), and in Hebrew the present tense agrees with the subject’s gender and number.

• מתנהגת = feminine singular behaves / is behaving
• מסכימה = feminine singular agrees / is agreeing

Compare:

• הוא מתנהג... לא מסכים = he behaves... doesn’t agree
• היא מתנהגת... לא מסכימה = she behaves... doesn’t agree

So the -ת and the overall form tell you the subject is feminine singular.

The dictionary form is להתנהג, meaning to behave or to conduct oneself.

In this sentence:

• מתנהג = masculine singular present
• מתנהגת = feminine singular present

So היא מתנהגת means she behaves or she is behaving, depending on context.

בנימוס is made of:

• ב־ = in / with
• נימוס = politeness / manners

So literally it means something like with politeness or in a polite manner.

Hebrew often uses ב־ + noun where English uses an adverb. So:

• מתנהגת בנימוס = behaves politely

Yes, תמיד (always) is commonly placed before the verb, and היא תמיד מתנהגת בנימוס sounds very natural.

Hebrew word order is somewhat flexible, so you may also see:

• היא מתנהגת תמיד בנימוס

But the version in your sentence is probably the most neutral and natural for everyday use.

אפילו means even.

It adds the idea that the next situation is especially noteworthy or slightly surprising. In other words, she behaves politely not only in normal situations, but even in a difficult one:

• אפילו כשהיא לא מסכימה = even when she doesn’t agree

So אפילו emphasizes the contrast.

Yes, it is commonly written as one word.

כשהיא = כש־ + היא

• כש־ = when
• היא = she

So כשהיא means when she.

A longer and more formal version would be:

• כאשר היא

But כשהיא is very common in normal Hebrew.

Because Hebrew does not use do/does as a helper verb the way English does.

In English:

• she doesn’t agree

In Hebrew:

• היא לא מסכימה

Literally, it looks more like she not agrees, but that is just the normal Hebrew structure. You usually negate a present-tense verb by putting לא before it.

Yes, you could, but it sounds more formal.

• היא לא מסכימה = everyday, normal spoken Hebrew
• היא אינה מסכימה = more formal, written, or elevated style

So in conversation, לא מסכימה is much more common.

Not always. Hebrew can leave that unstated if the context is already clear.

So היא לא מסכימה can simply mean:

• she doesn’t agree

If you want to say what or whom she disagrees with, you can add it:

• היא לא מסכימה איתו = she doesn’t agree with him
• היא לא מסכימה עם ההחלטה = she doesn’t agree with the decision

In your sentence, the focus is on her polite behavior, so the object is not necessary.

It most naturally describes a habit or general behavior.

Two things point to that:

• תמיד = always
• the present-tense forms מתנהגת and מסכימה

In Hebrew, the present tense can describe both:

• something happening now
• a general or repeated action

Here, because of תמיד, the meaning is clearly habitual: this is the way she usually behaves.

You would change the pronoun and the present-tense verb forms to masculine singular:

• הוא תמיד מתנהג בנימוס, אפילו כשהוא לא מסכים.

The changes are:

• היא → הוא
• מתנהגת → מתנהג
• כשהיא → כשהוא
• מסכימה → מסכים

Everything else stays the same.