حتى لو كانت الغرفة مفردة، تشمل سريرا إضافيا.

Yes:

• حتى لو = even if
• كانت = was / were, from كان; here it agrees with a feminine singular noun
• الغرفة = the room
• مفردة = single / single-occupancy
• تشمل = includes
• سريرا إضافيا = an extra bed

Grammatically, the sentence is:

• حتى لو كانت الغرفة مفردة = even if the room is single
• تشمل سريرا إضافيا = it includes an extra bed

The subject of تشمل is understood as the room.

حتى لو is a fixed expression meaning even if.

It introduces a concession: something is true despite the condition that follows.

So:

• لو كانت الغرفة مفردة = if the room were single
• حتى لو كانت الغرفة مفردة = even if the room were single / even if the room is single

This is stronger than a simple if. It means the second part still holds regardless of that condition.

Because الغرفة is a feminine singular noun.

The verb كان changes to match its subject:

• كان = masculine singular
• كانت = feminine singular

Since الغرفة is feminine, Arabic uses كانت.

This is very common in Arabic.

After لو and especially in expressions like حتى لو, Arabic often uses the past tense form to express a hypothetical or concessive idea, even when English uses the present.

So:

• حتى لو كانت الغرفة مفردة literally looks like even if the room was single
• but the natural meaning is even if the room is single

This is normal Arabic usage, not a real shift into past time.

مفردة is an adjective meaning single or individual, and it agrees with الغرفة.

Because الغرفة is:

• feminine
• singular
• definite

the adjective also appears in the matching feminine singular form: مفردة.

In hotel-style language, غرفة مفردة means single room.

Because Arabic verbs already include subject information.

تشمل means she includes or it includes for a feminine singular subject. Here the hidden subject is understood as هي, referring back to الغرفة.

So Arabic does not need to say:

• هي تشمل

unless you want extra emphasis.

In this sentence, تشمل by itself already tells you the subject is feminine singular.

For the same reason as كانت: it refers back to الغرفة.

Since الغرفة is feminine singular, the verb must match it:

• تشمل = feminine singular
• يشمل = masculine singular

So تشمل shows that the room is what includes the extra bed.

No preposition is needed.

شمل / يشمل is a directly transitive verb, meaning it takes a direct object by itself.

So Arabic says:

• تشمل سريرا إضافيا = it includes an extra bed

not:

• تشمل بسرير
• تشمل على سرير

That is just how this verb works.

Because this phrase is the direct object of تشمل, so it is in the accusative case.

In fully vocalized Arabic, it would be:

• سريرًا إضافيًّا

Both words are accusative:

• سريرًا = an extra bed
• إضافيًّا = extra

Without full vowel marks, this often appears as:

• سريرا إضافيا

So the ending changes because of grammar, not because the basic meaning changes.

Arabic does not have an indefinite article like a or an.

A noun is usually understood as indefinite when it:

• does not have ال
• and, in fully vocalized text, often has tanwīn

So:

• السرير = the bed
• سرير = a bed

Here سريرا إضافيا means an extra bed simply because the noun is indefinite.

Because they play different roles in the sentence.

• الغرفة = the room, meaning a specific room already known from context
• سريرا إضافيا = an extra bed, meaning one unspecified extra bed

This is very natural in Arabic:

• the room is a known item
• the extra bed is just something included with it

A fully vocalized version would be:

حتى لو كانتِ الغرفةُ مفردةً، تشملُ سريرًا إضافيًّا.

A few notes:

• الغرفةُ is the subject of كانت
• مفردةً is the predicate of كانت
• سريرًا إضافيًّا is the direct object phrase of تشمل
• In connected reading, كانتْ الغرفةُ is pronounced كانتِ الغرفةُ to avoid two sukūns in a row

For most learners, the unvowelled version is the one you will usually see in everyday texts.