Learn Hardcore Russian: В офисе начальница похвалила меня за отчёт, и её похвала подняла мне настроение. - At the office, the boss praised me for the report, and her praise lifted my mood.

В офисе is the prepositional case used with в to mean location (in the office).
В офис would be accusative and would mean direction/movement into the office (to/into the office), e.g. Я пошёл в офис.

What case is начальница, and why is it feminine?

Начальница is nominative singular (the subject of похвалила). It’s a feminine noun meaning (female) boss/supervisor.
Russian often has gendered job titles:

masculine: начальник
feminine: начальница
If the boss is a woman, начальница is natural. (Some workplaces still use the masculine form for women, but начальница is common.)

Why is the verb похвалила in that form?

Похвалила is:

past tense
feminine singular (agreeing with начальница)
perfective aspect (a completed action: she praised me once / gave praise)
If the subject were masculine: начальник похвалил меня.

Why is it меня and not мне after похвалила?

Похвалить takes a direct object in the accusative case: похвалить кого? что?
So: похвалила меня (me, accusative).
Мне (dative) would be used with verbs that require an indirect object, but not with похвалить in this meaning.

What does за отчёт mean here, and what case is отчёт?

За + accusative commonly means for (because of / in recognition of).
So за отчёт = for the report (i.e., because of my report / for my work on the report).
Отчёт is accusative singular (inanimate masculine, so it looks the same as nominative: отчёт).

Why is there a comma before и?

There are two independent clauses with different subjects: 1) В офисе начальница похвалила меня за отчёт
2) её похвала подняла мне настроение
In Russian, when и connects two full clauses, a comma is usually required (similar to English when clauses are long/independent).

Why repeat the idea with похвалила and then её похвала? Isn’t that redundant?

It’s a normal stylistic choice. The first clause states the event (she praised me), and the second names the event as a noun (her praise) to describe its effect (it lifted my mood).
Russian often uses this noun-style link to make the cause-effect relationship explicit.

What does её mean exactly, and how is it different from её in other contexts?

Её here means her (possessive): её похвала = her praise.
Important: её is also the accusative/genitive form of она (her as an object), but in её похвала it’s possessive.
Also, её is indeclinable (it doesn’t change for case): её книга, её книги, её книге, etc.

Why is it подняла мне настроение (with мне)?

This construction is: поднять кому настроение = to lift someone’s mood.

настроение is the direct object (accusative): what got lifted
мне is dative: whose mood it is (to me / for me)
So literally: (Her praise) lifted mood to me → natural English: lifted my mood / cheered me up.

Is поднять настроение the same as подняла мне настроение?

They’re closely related, but the grammar differs:

поднять настроение: focuses on the mood in general (often implied “someone’s” mood)
поднять мне настроение: explicitly says whose mood (dative мне)
You can also say подняла моё настроение (accusative + possessive adjective), which is also correct.

Could I replace подняла мне настроение with подняла мне дух or обрадовала меня?

Yes, but the nuance changes:

подняла мне настроение = made me feel more upbeat / improved my mood
подняла мне дух = boosted my spirits (often stronger, more “motivational”)
обрадовала меня = made me happy / glad (more direct emotional reaction)
Your sentence specifically emphasizes mood improvement, so подняла настроение fits well.

Is the word order flexible here? Could I say Начальница в офисе похвалила меня...?

Yes, Russian word order is flexible and changes emphasis:

В офисе начальница... emphasizes the setting (in the office)
Начальница в офисе... emphasizes the subject (the boss) a bit more
Both are correct; the original sounds natural for setting the scene first.

What’s the stress/pronunciation to watch out for in this sentence?

Common stress points:

начальни́ца (stress on -ни́-)
похвали́ла (stress on -ли́-)
отчёт (stress on -чёт)
похвала́ (stress on -ла́)
настрое́ние (stress on -е́-)