صديقتي تغسل يديها قبل كل وجبة، ولا تنسى الصابون.

صديقتي means my female friend.

It is made of:

• صديقة = a female friend
• ـي = my

So:

• صديقة → صديقتي = my female friend

A useful thing to notice: the feminine ending ة changes to ت when a suffix is attached, so صديقة becomes صديقتي.

تغسل is the present/imperfect form of the verb غسل = to wash.

Here it means she washes.

The prefix تـ can mark several forms in Arabic, but in this sentence it is understood as she because the subject is صديقتي, which is feminine singular.

So:

• غسل = he washed / the basic past stem
• تغسل = she washes / is washing

In a sentence like this, the imperfect usually gives a habitual meaning, so it matches English washes well.

Arabic often leaves the subject pronoun unstated because the verb already shows who the subject is.

So تغسل already tells you she washes, and تنسى tells you she forgets.

Because the subject صديقتي is already mentioned, Arabic does not need to add هي.

English needs she, but Arabic often does not.

Because Arabic often uses the dual for body parts that come in pairs.

So instead of using a plural, Arabic commonly says the equivalent of her two hands.

Here:

• يد = hand
• يدان / يدين = two hands
• يديها = her two hands

In natural English, we simply say her hands, but Arabic is being more specific grammatically.

Also, يديها is in the form used after a verb as a direct object.

This is because of case in the dual.

For the dual, Arabic has:

• يدان / with suffix يداها in the nominative
• يدين / with suffix يديها in the accusative or genitive

Since يديها is the direct object of تغسل, it takes the accusative-type dual form, so you get يديها.

So literally the structure is:

• تغسل يديها = she washes her two hands

قبل means before.

Then you have:

• كل = every / each
• وجبة = meal

So:

• قبل كل وجبة = before every meal

This is a very common Arabic pattern:

• قبل كل درس = before every lesson
• بعد كل يوم = after every day
• كل أسبوع = every week

Because in Arabic, كل + singular noun is the normal way to say every / each.

So:

• كل يوم = every day
• كل مرة = every time
• كل وجبة = every meal

Arabic does not normally use a plural here. The singular noun after كل gives the distributive meaning: one by one, each instance.

Here ولا means and not or nor.

The sentence has two linked ideas:

• صديقتي تغسل يديها قبل كل وجبة
• ولا تنسى الصابون

So the overall sense is:

• My friend washes her hands before every meal, and she does not forget the soap
• or more naturally: ..., nor does she forget the soap

It is simply و + لا:

• و = and
• لا = not

Because this verb comes from نسي = to forget, which is a weak verb.

In the imperfect, the form here is:

• تنسى = she forgets

It is pronounced tansā.

The final ى is alif maqṣūra, and it represents a final long ā sound.

So even though it looks unusual at first, تنسى is the normal spelling for this verb form.

الصابون literally means the soap.

Arabic often uses the definite article ال in places where English may simply say soap in a general sense.

So in a sentence about handwashing, الصابون sounds very natural: it refers to the expected or typical soap used for washing.

Compare:

• الصابون = the soap / soap in the general expected sense
• صابون = soap, some soap, an indefinite soap item

In context, ولا تنسى الصابون naturally means and she doesn’t forget the soap or simply and she doesn’t forget soap.

Yes. Arabic allows both orders.

You could also say:

• تغسل صديقتي يديها قبل كل وجبة، ولا تنسى الصابون.

Both are grammatical.

The version you were given starts with صديقتي, which puts the focus first on my friend. That is very natural in simple descriptive sentences.

So:

• صديقتي تغسل... = more subject-first
• تغسل صديقتي... = more verb-first

Both are acceptable in Modern Standard Arabic.