היא ניסתה לפנק את עצמה בארוחת ערב טובה אחרי יום ארוך.

Because the subject is היא (she), and ניסתה is the 3rd person feminine singular form in the past tense of לנסות (to try).

• הוא ניסה = he tried
• היא ניסתה = she tried

So the -ה ending tells you the verb matches a feminine singular subject.

After ניסה / ניסתה (tried), Hebrew normally uses an infinitive to say what someone tried to do.

So:

• ניסתה לפנק = she tried to pamper / treat

This works like English tried to + verb.

Other examples:

• ניסיתי להבין = I tried to understand
• הם ניסו לעזור = they tried to help

לפנק means something like:

• to pamper
• to spoil
• to treat

In this sentence, the best feel is probably to treat herself or to pamper herself.

It often has a warm, indulgent tone: doing something nice, enjoyable, or comforting for someone.

For example:

• לפנק את הילדים = to spoil/pamper the children
• לפנק את עצמי בקפה טוב = to treat myself to a good coffee

Hebrew usually expresses herself / himself / myself with עצמי / עצמך / עצמו / עצמה and so on.

Here:

• עצמה = herself

But because it is the direct object of the verb לפנק, Hebrew also uses את before it:

• לפנק את עצמה = to pamper herself

So:

• את marks a definite direct object
• עצמה is the reflexive word herself

Good question. Hebrew את has two completely different jobs:

1. את = you (feminine singular)
2. את = marker of a definite direct object

In this sentence, it is the direct object marker, not the pronoun you.

So in:

• לפנק את עצמה

the את does not mean you. It simply introduces the definite object עצמה (herself).

This part means with a good dinner or by having a good dinner.

Breakdown:

• ב־ = in / with / by
• ארוחת ערב = dinner, literally evening meal
• טובה = good

So the whole phrase shows the means or way she treated herself:

• She treated herself with a good dinner
• more natural English: She treated herself to a good dinner

The Hebrew ב־ here is very common for expressing by means of or with something.

Because this is a construct phrase in Hebrew.

• ארוחה = meal
• ערב = evening

When Hebrew says meal of evening, it uses the construct form:

• ארוחת ערב

This is the normal way to say dinner / evening meal.

Similar examples:

• בית ספר = school, literally house of book
• יום הולדת = birthday, literally day of birth

So ארוחת is the construct form of ארוחה.

Because it describes ארוחה (meal), which is a feminine singular noun.

Even though ערב is masculine, in the construct phrase ארוחת ערב, the head noun is ארוחה, so the adjective agrees with that noun:

• ארוחה טובה = a good meal
• ארוחת ערב טובה = a good dinner

That is why the adjective is טובה, not טוב.

Because the sentence means a good dinner, not the good dinner.

Hebrew leaves the phrase indefinite here:

• בארוחת ערב טובה = with a good dinner

If it were definite, you would mark definiteness differently, for example:

• בארוחת הערב הטובה = with the good dinner

So the lack of ה־ shows this is indefinite.

Literally it means after a long day.

Breakdown:

• אחרי = after
• יום = day
• ארוך = long

The adjective ארוך is masculine singular because יום is masculine singular.

So:

• יום ארוך = a long day

Hebrew word order is fairly flexible, but this sentence follows a very natural pattern:

• היא = subject
• ניסתה = main verb
• לפנק את עצמה = infinitive phrase
• בארוחת ערב טובה = how / by what means
• אחרי יום ארוך = time background

So the sentence moves from:

1. who
2. what happened
3. what she tried to do
4. how she did it
5. when/under what circumstances

That sounds natural and smooth in Hebrew.

Yes, you may hear forms with עם (with), especially in modern speech, but בארוחת ערב טובה is very natural and elegant here.

Compare:

• לפנק את עצמה בארוחת ערב טובה = treat herself with / by means of a good dinner
• לפנק את עצמה עם ארוחת ערב טובה = treat herself with a good dinner

The version with ב־ often sounds a bit more idiomatic in this kind of sentence.

Yes, functionally that is a good way to think about it.

Hebrew does not use a special reflexive verb form here. Instead, it uses:

• the normal verb לפנק
• plus the reflexive object את עצמה

So literally it is:

• to pamper herself

This is common in Hebrew:

• הוא ראה את עצמו = he saw himself
• היא הכינה לעצמה קפה = she made herself coffee
• אני שואל את עצמי = I ask myself

So yes, the meaning is reflexive, even though the grammar is built with a normal verb plus עצמה.