Ей предстоит принять решение.

Because this construction uses the dative case for the person affected.

With предстоять, Russian often says something like to someone lies ahead to do something. So the person is not the grammatical subject in the usual nominative sense.

• ей = to her
• она = she

So Ей предстоит принять решение is literally closer to To her there lies ahead the task of making a decision.

Предстоит is the 3rd person singular form of предстоять.

In this sentence it means something like:

• is still ahead
• has yet to
• will have to face
• is faced with

So the sentence suggests that making the decision is something awaiting her.

It often sounds a bit more formal or literary than a very plain everyday phrasing.

Grammatically, предстоит is present tense.

But in meaning, it usually points to the future, because it describes something that is ahead of someone.

So:

• grammar: present
• sense: future/upcoming

That is very normal in Russian with this verb.

Because предстоять commonly takes an infinitive to describe the action that awaits someone.

Pattern:

• кому? + предстоит + infinitive

Examples:

• Нам предстоит много работать. = We have a lot of work ahead of us.
• Ему предстоит выступить. = He still has to speak / He is to speak.

So принять names the action she has ahead of her.

Because принять is perfective, and here Russian views the action as a single completed result: she must make/reach a decision.

• принять = complete the act
• принимать = process, repetition, habit, or ongoing action

In this sentence, the focus is on the fact that a decision must be arrived at, so принять is the natural choice.

Решение is in the accusative singular, because it is the direct object of принять.

However, for many inanimate neuter nouns, the accusative looks exactly like the nominative.

So:

• nominative: решение
• accusative: решение

Same form, different function.

Not in this context. Принять решение is a very common Russian collocation meaning to make a decision or to take a decision.

So принять does not always mean only accept. Depending on context, it can mean things like:

• take
• adopt
• receive
• accept

Here, принять решение is best understood as a set expression meaning make a decision.

Not in the usual noun/pronoun in nominative way.

The sentence is built around the idea that the action itself is what lies ahead. In simpler learner terms, you can think of it as:

• To her lies ahead: making a decision

So ей is not the subject; it is the person affected, in the dative. The construction is often treated as impersonal or semi-impersonal in practice.

These are similar, but not identical.

• Ей предстоит принять решение
  = a decision lies ahead of her; this is the task/situation awaiting her

• Ей нужно принять решение
  = she needs to make a decision; practical necessity

• Она должна принять решение
  = she must make a decision; stronger obligation, duty, or expectation

So предстоит often sounds a bit less like a direct command and more like this is what she is going to have to deal with.

Yes, Russian word order is flexible, but the neutral order here is:

Ей предстоит принять решение.

That order sounds natural and straightforward.

You can change the order for emphasis, but not every rearrangement sounds equally natural in isolation. For a learner, this basic order is the safest and most standard.

It is not extremely formal, but предстоит is a bit more elevated or bookish than very plain everyday alternatives.

For example:

• Ей предстоит принять решение. = slightly more formal/neutral narrative style
• Ей нужно принять решение. = more everyday
• Она должна решить. = shorter, more direct

So you may see предстоит often in writing, news, narration, or more polished speech.

The main stresses are:

• Ей
• предстои́т
• приня́ть
• реше́ние

A rough pronunciation guide:

• Ей ≈ yey
• предстои́т ≈ pred-sta-EET
• приня́ть ≈ pree-NYAT'
• реше́ние ≈ ree-SHE-ni-ye

For Russian, the stress placement is important, especially in предстои́т, приня́ть, and реше́ние.