Это мастер, у которой всегда аккуратные брови и длинные ресницы.

Мастер is grammatically a masculine noun, but in Russian many job titles are still used in the masculine form even when they refer to a woman. This is very common in professional and service contexts.

So here мастер can mean a female specialist too. The sentence shows that the person is female through которой, which is feminine.

Here это does not mean this as an agreeing adjective. It means this is or here is.

So:

• Это мастер = This is a specialist / This is the master
• Этот мастер = this specialist (using a demonstrative adjective)

Because мастер is grammatically masculine, standard Russian would normally use этот if you meant this specialist. But in your sentence, это is just the fixed identifying word this is.

Literally, у которой means something like at whom. But in Russian, у + genitive is the normal way to express possession.

So:

• у неё длинные ресницы = she has long eyelashes
• мастер, у которой... = the specialist who has...

Here которой is:

• feminine
• singular
• genitive

It is genitive because it comes after у.

Russian usually does not use a direct verb equivalent to English have/has in ordinary sentences like this. Instead, it normally uses the у + genitive pattern:

• у неё длинные ресницы = she has long eyelashes

Using иметь here would sound too formal, bookish, or unnatural in everyday speech.

Also, the word есть is often omitted in this kind of present-tense description. So у которой всегда аккуратные брови и длинные ресницы sounds natural.

Russian normally leaves out the present-tense verb to be.

So:

• Это мастер literally looks like This specialist
• but it means This is a specialist

This is completely normal Russian grammar.

Because they describe plural nouns:

• аккуратные брови = neat eyebrows
• длинные ресницы = long eyelashes

In Russian, adjectives agree with the nouns they describe in number, gender, and case. Since брови and ресницы are plural here, the adjectives are plural too.

In the Russian possession pattern у + genitive, the person who possesses something goes into the genitive, but the thing possessed usually stays in the nominative.

So in:

• у которой = who has / at whom
• брови and ресницы are the things possessed

That is why you get:

• у неё красивые глаза
• у него длинные волосы
• у которой аккуратные брови и длинные ресницы

No. This is a classic false friend.

Аккуратный usually means:

• neat
• tidy
• careful
• well-groomed

So аккуратные брови means neat / well-shaped / well-groomed eyebrows, not accurate eyebrows.

Because у которой всегда аккуратные брови и длинные ресницы is a relative clause describing мастер.

Russian normally separates this kind of subordinate clause with a comma:

• Это мастер, у которой...

So the comma is required here.