На юбке появилась складка, и я решила её погладить.

Because the crease is understood as being on the surface of the skirt.

• на юбке = on the skirt
• в юбке = in the skirt

For marks, wrinkles, folds, stains, buttons, pockets, and similar things on clothing, Russian often uses на.

So На юбке появилась складка is the natural way to say that a fold/crease appeared on the skirt.

Because на here requires the prepositional case when it means location.

The dictionary form is юбка.
Its prepositional singular is юбке.

So:

• юбка = skirt
• на юбке = on the skirt

Because складка is the subject of the verb появилась.

The sentence structure is basically:

• На юбке = location
• появилась складка = a crease appeared

Even though English often starts with A crease appeared..., Russian can naturally begin with the location: На юбке появилась складка.

Because the subject, складка, is feminine.

In the past tense, Russian verbs agree with gender and number:

• masculine: появился
• feminine: появилась
• neuter: появилось
• plural: появились

Since складка is feminine singular, the verb is появилась.

Because the speaker is female, or at least the speaker is being referred to as feminine.

Russian past tense verbs also agree with the gender of the subject:

• я решил = I decided (male speaker)
• я решила = I decided (female speaker)

So я решила tells you that the speaker is female.

Here складка means a fold, crease, or wrinkle-like line in fabric.

In clothing contexts, it can be translated in different ways depending on the situation:

• fold
• crease
• sometimes wrinkle

A native English speaker might think of crease as the most natural translation here.

Yes, погладить can mean to stroke/pet someone or something, but here it means to iron or to smooth with an iron.

Russian uses the same verb family:

• гладить кошку = to pet/stroke a cat
• гладить рубашку = to iron a shirt

The context makes the meaning clear. Since we are talking about a skirt and a crease, погладить means to iron.

Because after решить in the sense of to decide, Russian normally uses an infinitive.

So:

• я решила погладить её = I decided to iron it

This is very similar to English decided to do something.

Other examples:

• Я решил уйти. = I decided to leave.
• Она решила купить платье. = She decided to buy a dress.

Because the sentence presents the actions as single, completed events.

• появилась = appeared, came into being
• решила = made the decision
• погладить = to iron it as one completed action

This gives the sentence a clear sequence:

1. a crease appeared
2. I decided
3. I would iron it

If you used imperfective forms, the meaning would shift more toward process, repetition, or background description.

For example:

• появлялась could suggest something recurring or ongoing
• решала could suggest the process of deciding
• гладить could focus more on the activity rather than the completed result

Grammatically, её could refer to either юбку or складку, because both are feminine singular nouns.

So yes, there is some ambiguity.

In practice:

• many people will understand её as юбку, because гладить юбку is a very normal phrase
• but the immediate context is the складка, so some readers may momentarily connect it with the crease

If you want to remove ambiguity, Russian can make it clearer:

• ...и я решила погладить юбку. = ...and I decided to iron the skirt.
• ...и я решила разгладить складку. = ...and I decided to smooth out / iron out the crease.

Because неё is used after a preposition, while её is used without one.

Compare:

• Я погладила её. = I ironed it / I stroked her.
• Я думала о ней. = I thought about her.
• Я подошла к ней. = I went up to her.

So here there is no preposition before the pronoun, which is why её is correct.

Yes. In ordinary writing, ё is often replaced by е, so её is very often written ее.

Both represent the same word here.

However, for learners, writing ё is helpful because it shows the correct pronunciation and avoids confusion.

Yes. Russian word order is flexible.

You could also say:

• Складка появилась на юбке, и я решила её погладить.

That version is also correct, but the focus changes slightly.

• На юбке появилась складка starts with the skirt as the setting/topic
• Складка появилась на юбке starts with the crease itself

Russian often uses word order to manage emphasis rather than basic grammar.

Sometimes, yes.

• погладить юбку = to iron the skirt
• разгладить складку = to smooth out / iron out the crease

So if the idea is specifically to remove the crease, разгладить складку can sound more precise.

The original sentence is still natural, especially if the intended idea is I decided to iron the skirt because a crease had appeared.