मेरी बहन मुझसे तेज़ बोलती है, लेकिन मैं उससे धीरे लिखती हूँ।

Because बहन is a feminine noun in Hindi, so the possessive my must agree with it.

• मेरा = my, used with masculine singular
• मेरी = my, used with feminine singular
• मेरे = my, used with masculine plural or certain oblique forms

So:

• मेरा भाई = my brother
• मेरी बहन = my sister

Here, बहन is feminine, so मेरी is correct.

मुझसे is the oblique form of मैं with से.

In Hindi, pronouns often change form before postpositions like से, को, में, etc.

So:

• मैं = I
• मुझ- = oblique stem
• मुझसे = from me / than me / by me, depending on context

You cannot normally say मैं से in standard Hindi.

Similar examples:

• तुम → तुमसे
• वह → उससे
• हम → हमसे

In this sentence, मुझसे means than me.

In Hindi, से is commonly used to mark comparison.

So the pattern is:

X Y से [adjective/adverb] ...
= X is more [adjective/adverb] than Y

Examples:

• राम मोहन से लंबा है। = Ram is taller than Mohan.
• वह मुझसे तेज़ दौड़ता है। = He runs faster than me.
• मेरी बहन मुझसे तेज़ बोलती है। = My sister speaks faster than me.

So in your sentence:

• मुझसे = than me
• उससे = than her

Because Hindi often expresses comparison simply with:

[thing/person] + से + adjective/adverb

So तेज़ already works as fast/faster depending on context.

• वह तेज़ बोलती है। = She speaks fast.
• वह मुझसे तेज़ बोलती है। = She speaks faster than me.

Likewise:

• मैं उससे धीरे लिखती हूँ। = I write more slowly than her.

Hindi does have words like ज़्यादा and और, but they are not required in basic comparisons like this.

Because the subjects in both clauses are feminine.

First clause:

• मेरी बहन ... बोलती है
• Subject = बहन = feminine singular
• So the verb uses the feminine singular habitual form: बोलती है

Second clause:

• मैं ... लिखती हूँ
• The speaker uses लिखती, which is feminine singular
• That tells us the speaker is female

Compare:

• masculine: बोलता है, लिखता हूँ
• feminine: बोलती है, लिखती हूँ

Yes. In normal Hindi, this strongly indicates that the speaker is female.

• मैं लिखता हूँ = I write (said by a male speaker)
• मैं लिखती हूँ = I write (said by a female speaker)

So from this sentence, we can infer:

• the speaker’s sister is female, obviously
• the speaker is also female, because she says लिखती हूँ

Here उससे refers to the sister mentioned earlier.

So:

• मेरी बहन मुझसे तेज़ बोलती है = My sister speaks faster than me
• लेकिन मैं उससे धीरे लिखती हूँ = but I write more slowly than her

The pronoun वह becomes उस- before postpositions:

• वह = he/she/that
• उससे = from him/her, than him/her

In this sentence, context makes it clear that उससे means than her, referring back to my sister.

Because धीरे is functioning as an adverb: slowly.

It modifies the verb लिखती हूँ.

So:

• धीरे लिखती हूँ = write slowly
• तेज़ बोलती है = speak fast / speak quickly

This is a very common placement in Hindi: adverb + verb

Examples:

• वह अच्छा गाती है। = She sings well.
• मैं जल्दी उठता हूँ। = I wake up early.
• वह धीरे बोलता है। = He speaks slowly.

Because तेज़ and धीरे can directly function as adverbs in everyday Hindi.

So these are natural:

• तेज़ बोलना = to speak fast
• धीरे लिखना = to write slowly

About the alternatives:

• तेज़ी से also means quickly/rapidly, but often sounds a bit more formal or emphatic
• धीरे से often means softly/gently rather than just slowly, depending on context

So in this sentence:

• तेज़ बोलती है is natural and simple
• धीरे लिखती हूँ is also natural and simple

Hindi word order is flexible, but this order is very natural.

The basic idea is:

• comparison phrase: मुझसे / उससे
• adverb: तेज़ / धीरे
• verb: बोलती है / लिखती हूँ

So:

• मेरी बहन मुझसे तेज़ बोलती है
• मैं उससे धीरे लिखती हूँ

You may also hear slight variations, but this version sounds smooth and standard.

For example, these are also understandable:

• मेरी बहन तेज़ बोलती है मुझसे
• मैं धीरे लिखती हूँ उससे

But they are less neutral or less standard in careful teaching contexts.

लेकिन means but.

It connects the two contrasting ideas:

• My sister speaks faster than me
• but I write more slowly than her

So लेकिन introduces contrast.

Other common Hindi words for but include:

• पर
• मगर
• लेकिन

All are common, though लेकिन is a very standard textbook choice.

तेज़ has a wider range of meanings than the English word fast.

Depending on context, it can mean:

• fast
• quick
• sharp
• strong
• intense

In तेज़ बोलती है, it usually means speaks fast or sometimes speaks loudly/forcefully, depending on context. Since this sentence is clearly a comparison, the intended meaning is most naturally speaks faster.

So learners should think of तेज़ as a flexible word whose exact meaning depends on what it modifies.

Yes. Hindi does not need an extra verb like does here.

English often says:

• My sister speaks faster than I do
• I write more slowly than she does

Hindi simply uses से with the comparison target:

• मुझसे = than me
• उससे = than her

The rest is understood from context.

So मैं उससे धीरे लिखती हूँ is a completely natural Hindi way to say I write more slowly than her.

Not in this exact form.

Because it says:

• मैं ... लिखती हूँ

That is feminine. A male speaker would say:

मेरी बहन मुझसे तेज़ बोलती है, लेकिन मैं उससे धीरे लिखता हूँ।

So the only change would be:

• लिखती हूँ → लिखता हूँ

Everything else could stay the same.