Нет бы ей использовать мебельный чехол — она поцарапала стол.

Нет бы is an idiomatic expression of reproach or criticism. It means something like:

• she could have at least...
• instead, she should have...
• why didn’t she just...

So Нет бы ей использовать мебельный чехол — она поцарапала стол means roughly:

• She should have used a furniture cover, but instead she scratched the table.

The phrase is emotionally colored: the speaker is annoyed and thinks the better choice was obvious.

Because the construction is:

нет бы + dative + infinitive

So:

• ей = to her / for her
• использовать = to use

Literally, the grammar is something like:

• Why wasn’t it for her to use...
• or She could have just used...

But in natural English, you would not translate it literally. The important thing is that нет бы regularly takes the person in the dative case.

Examples:

• Нет бы мне промолчать. = I should have just kept quiet.
• Нет бы ему позвонить. = He could have just called.

Because after нет бы, Russian normally uses the infinitive to name the action that would have been the better idea.

So:

• ей использовать = for her to use
• ему подождать = for him to wait
• нам проверить = for us to check

This is part of the fixed pattern:

Нет бы + dative + infinitive

It does not mean the action actually happened. It refers to the action that would have been smarter or more appropriate.

Yes, it is fairly common in speech and informal writing. The tone is usually:

• colloquial
• critical
• complaining
• sometimes sarcastic

It often sounds like the speaker is frustrated because someone did the wrong thing instead of the obvious right thing.

So this sentence does not sound neutral. It sounds more like:

• And instead of using a cover, she went and scratched the table.

If you want a neutral version, you would say something more direct, such as:

• Ей стоило использовать мебельный чехол.
• Она могла использовать мебельный чехол.

Those are less emotional than нет бы.

The dash links two ideas with a strong contrast:

• the sensible thing she should have done
• the bad thing she actually did

So the structure is:

• Нет бы ей использовать мебельный чехол — она поцарапала стол.

This feels like:

• Instead of using a furniture cover, she scratched the table.

A conjunction like а could also appear in similar sentences:

• Нет бы ей использовать мебельный чехол, а она поцарапала стол.

The dash makes the contrast a bit sharper and more dramatic.

Literally, it means a furniture cover.

• мебельный = furniture-related
• чехол = cover, case, protective cover

So мебельный чехол is a cover used to protect furniture.

A learner may notice that English often prefers a noun-noun structure like furniture cover, while Russian often uses an adjective + noun structure:

• мебельный чехол
• compare:
  • кухонный стол = kitchen table
  • зимняя одежда = winter clothing

Поцарапала is the past tense, feminine singular form of поцарапать, meaning to scratch.

It agrees with the implied subject она, so:

• она поцарапала = she scratched

Стол is in the accusative case because it is the direct object:

• поцарапать что? → стол

For an inanimate masculine noun like стол, the accusative looks the same as the nominative:

• nominative: стол
• accusative: стол

So there is nothing unusual there; that is normal Russian grammar.

Sometimes yes, but only if you keep the tone in mind.

If only she had used... can work, because it expresses regret about what would have been better. But нет бы usually has more of a complaining / reproachful flavor than a pure wish.

So depending on context, good translations include:

• She should have used a furniture cover.
• Why didn’t she just use a furniture cover?
• Instead of using a furniture cover, she scratched the table.
• She could have at least used a furniture cover.

So if only is possible, but it is not always the best match for the emotional tone.

Yes, Russian word order is flexible, and with нет бы you may hear variants, especially in speech.

For example:

• Нет бы ей использовать мебельный чехол...
• Ей бы мебельный чехол использовать...
• Нет бы использовать мебельный чехол...
  if the person is clear from context

But the exact nuance can shift a little depending on emphasis.

The original version is very natural and clearly presents the pattern:

нет бы + dative + infinitive

That makes it a good textbook example.

Yes. It is very common to use it about yourself when criticizing your own choice after the fact.

For example:

• Нет бы мне взять зонт. = I should have taken an umbrella.
• Нет бы нам заранее проверить адрес. = We should have checked the address beforehand.

So the construction is not limited to talking about other people. It can express:

• annoyance with someone else
• annoyance with yourself
• ironic hindsight in general

No. It is just one natural choice, meaning to use. Depending on context, Russian might also use other verbs, such as:

• надеть чехол = to put the cover on
• накрыть стол чехлом = to cover the table with a cover
• защитить стол = to protect the table

So:

• Нет бы ей накрыть стол чехлом...
• Нет бы ей защитить стол...

could also make sense, depending on what exactly happened.

The important grammar point is not the specific verb, but the construction:

нет бы + dative + infinitive