Ona denerwuje się przed egzaminem, ale uczy się regularnie.

Się is a reflexive particle, and in this sentence it is part of two very common Polish verbs:

• denerwować się = to get nervous / to be anxious / to worry
• uczyć się = to study / to learn

You usually learn these as whole verb expressions, not as a normal verb plus a separate word you can freely remove.

A useful comparison:

• denerwować kogoś = to annoy someone
• denerwować się = to get nervous / be upset

and

• uczyć kogoś = to teach someone
• uczyć się = to study / learn

So się changes the meaning and is essential here.

Not in normal English. Even though się is historically reflexive, in many Polish verbs it does not translate literally as herself/myself/yourself.

Here, ona denerwuje się means something like:

• she gets nervous
• she is nervous
• she worries

It does not usually mean she annoys herself.

Because the preposition przed takes the instrumental case when it means before or in front of.

So:

• dictionary form: egzamin
• after przed: egzaminem

That is why the noun changes form.

In this sentence:

• przed egzaminem = before the exam

It is the instrumental singular form of egzamin.

For many masculine nouns, the instrumental singular ending is -em, so:

• egzamin → egzaminem
• student → studentem
• dom → domem

Here that case is required by przed.

Usually, no. Polish often drops subject pronouns because the verb ending already shows the person and number.

So you could simply say:

• Denerwuje się przed egzaminem, ale uczy się regularnie.

That still clearly means She gets nervous before the exam, but she studies regularly.

Including ona can add:

• emphasis
• contrast
• clarity in context

For example, if you are contrasting her with someone else, ona makes more sense.

They are both in the present tense, third person singular:

• ona denerwuje się = she gets nervous / she is getting nervous
• ona uczy się = she studies / she is studying

Because these are imperfective verbs, the Polish present tense can describe:

• something happening now
• a repeated habit
• a general tendency

In this sentence, uczy się regularnie sounds clearly habitual: she studies regularly.

The verb uczyć się can mean both to learn and to study, depending on context.

Here, because of regularnie and the mention of an exam, the most natural English translation is:

• she studies regularly

If the context were different, uczyć się could also mean:

• to learn something
• to be learning

So this is a good example of how context determines the best English equivalent.

This is an aspect difference:

• uczyć się = imperfective, focusing on the process, repetition, or duration
• nauczyć się = perfective, focusing on completion or successful learning

Examples:

• Uczy się polskiego. = She is studying Polish.
• Nauczyła się polskiego. = She learned Polish / She has mastered Polish.

In your sentence, uczy się regularnie fits because it describes an ongoing habit, not a completed result.

They are related but not the same:

• denerwować kogoś = to annoy / upset someone
• denerwować się = to get nervous / worry / be upset

Compare:

• Egzamin ją denerwuje. = The exam makes her nervous / annoys her.
• Ona denerwuje się przed egzaminem. = She gets nervous before the exam.

This is a very common pattern in Polish: adding się can create a different verb meaning.

Polish word order is more flexible than English. Putting regularnie at the end is completely natural.

This sentence order is standard:

• Ona denerwuje się przed egzaminem, ale uczy się regularnie.

You could also move parts around for emphasis, but some versions sound more marked than others.

For example:

• Ona regularnie uczy się przed egzaminem would suggest something slightly different in meaning and focus.
• Uczy się regularnie is the most neutral way to say she studies regularly.

So the end position is normal and idiomatic here.

Polish does not use articles like English a/an/the.

So egzamin or egzaminem can mean:

• an exam
• the exam

The exact meaning depends on context.

In this sentence, przed egzaminem is usually understood as before the exam or before an exam, depending on the situation.

Yes, depending on context, that is a very natural interpretation.

Denerwować się often covers ideas like:

• to get nervous
• to worry
• to be stressed
• to be upset

Before an exam, English speakers often say:

• She gets nervous before the exam
• She gets stressed before the exam

Both are reasonable ways to understand the Polish.

It breaks down very neatly:

• Ona = she
• denerwuje się = gets nervous / is nervous
• przed egzaminem = before the exam
• ale = but
• uczy się regularnie = studies regularly

So grammatically it is:

subject + verb + phrase of time/circumstance + but + verb + adverb

A useful thing to notice is that Polish often builds meaning through:

• verb forms
• reflexive się
• case endings like -em

rather than through articles or very fixed word order.