She was raped by a kaafir during the day in Ramadaan

Rape implies force and coercion, and the one
who is forced to do something is not held to account for it. Allaah says (interpretation of the meaning): 

“Whoever disbelieved in Allaah after his
belief, except him who is forced thereto and whose heart is at rest with Faith; but such as open their breasts to disbelief, on them is wrath from
Allaah, and theirs will be a great torment”
[al-Nahl 16:106]

This verse indicates that those who speak words of kufr because they are forced to do so are
free of sin and blame, so long as their hearts remained at rest with faith. If this is the case with kufr, which is the most serious of haraam
things, then it applies even more so to things that are less severe: the person who is forced to do them is not held to account for it. 

The Prophet (peace and blessings of
Allaah be upon him) said: “Allaah has forgiven my ummah for mistakes, forgetfulness and that which they are forced to do.” Narrated by Ibn Maajah,
2033; classed as saheeh by al-Albaani in Saheeh Sunan Ibn Maajah, 1664. 

So if a woman who was raped did her utmost to
resist, but she was not able to escape, there is no sin on her; her fast is valid and she does not have to make it up or offer any kafaarah
(expiation). 

Imam Ahmad (may Allaah have mercy on him)
said: 

Everything that overwhelms a fasting person,
he does not to make it up or do anything else. Al-Mughni, 4/376. 

Shaykh Ibn Baaz was asked about a man who has intercourse with his wife when she does not want
to. He replied: 

… If the woman is forced to do it then there is no sin on her and her fast is still valid, but
if she let him do it then she has to make up that day and also repent, but she does not have to offer expiation. 

Fataawa al-Shaykh Ibn Baaz,
15/310. 

Shaykh Ibn ‘Uthaymeen said in al-Sharh
al-Mumti’ (6/414) on the ruling on having intercourse during the day in Ramadaan: 

If the woman is excused because of ignorance
or forgetfulness, or because she was forced to do it, then she does not have to make it up and she does not have to offer expiation. 

We take this opportunity to advise women to
fear Allaah and to avoid mixing with men, especially kaafirs and the immoral ones among them, and to keep away from everything that may attract
men to them of tabarruj (wanton display), soft speech and flirtatious speech and behaviour. They should choose suitable times and avoid doubtful
places or situations. They should adhere to the commands of Allaah and observe hijab and cover themselves, because that will protect them and is
good for them in this world and in the hereafter.

 And Allaah is the one Whom we ask to set the
Muslims’ affairs straight.

 And Allaah knows best.