She admitted to zina and is going to get married, and is afraid of being exposed to shame

The calamity asked about here is one of the outcomes of
haraam relationships: making acquaintances, promises, lies, love and
infatuation, followed by immoral actions, ruined lives, disgrace, scandal
and shame. Sincere advisers are still shouting at the heedless to wake up
and telling the deluded to pay attention, whilst the proponents of free
mixing and evil are still defending their stance, claiming that there is
nothing wrong with these relationships, and that it is not necessary to
impose restrictions on boys and girls. The one who will suffer as a result
of this sin and because of the scandal, worries and anxiety is this deceived
girl, who followed the footsteps of the Shaytaan and was fooled by wishes
and false promises, so she went against the command of her Lord to stay in
her house, lower her gaze, avoid speaking softly and adhere to hijab. Verily
to Allah we belong and to Him we will return. Hoe regrettable it is for the
Muslims that this corruption exists in their societies and has crept into
their houses, with the neglect of fathers and mothers, brothers and
sisters. 

How abhorrent is zina and how awful its consequences in this
world and in the Hereafter. Hence the punishment for the one who does it is
either flogging or stoning, along with the painful punishment in the fire of
Hell. 

Allah, may He be exalted, says (interpretation of the
meaning):

“The woman and the man guilty of illegal sexual
intercourse, flog each of them with a hundred stripes. Let not pity withhold
you in their case, in a punishment prescribed by Allah, if you believe in
Allah and the Last Day. And let a party of the believers witness their
punishment.”

[an-Noor 24:2]

“And come not near to the unlawful sexual intercourse.
Verily, it is a Fahishah (i.e. anything that transgresses its limits (a
great sin)), and an evil way (that leads one to Hell unless Allah forgives
him)”

[al-Isra’ 17:32]. 

In the hadeeth of the dream that the Prophet (blessings and
peace of Allah be upon him) saw, he said: “…So we went on, and came to
something like a tannoor (a kind of oven, lined with clay, usually used for
baking bread).  – I think he said: In it there was much noise and voices. –
We  looked into it and saw naked men and  women. A flame of fire was
reaching them from underneath, and when it reached them, they cried out
loudly. I asked them, ‘Who are these?’ They said to me, ‘Move on, move on!’
… I said to them, ‘I have seen many wonders this night. What do all these
things mean that I have seen?’ They said: ‘We will tell you. … The naked men
and women whom you saw in a structure that resembled an oven are the
adulterers and adulteresses.’”

Narrated by al-Bukhaari in Baab Ithm az-Zunaat, no.
7047 

Hence what this girl has to do is repent sincerely to Allah,
may He be exalted, regret it a great deal, pray for forgiveness, and resolve
never to do such a thing again, in the hope that Allah may forgive her and
pardon her. She should also offer a great deal of supplication (du‘aa’) and
beseech Allah, may He be exalted, to conceal her and not expose her in this
world or in the Hereafter, and to suffice her against the evil of that
evildoer. She should choose the times when supplications are answered, such
as the last third of the night, the time between the adhaan and iqaamah, and
the last hour of Friday. She should also do a lot of acts of worship,
especially praying and giving charity. And she should think positively of
her Lord, may He be glorified, because He said in the hadeeth qudsi: “I am
as My slave thinks I am, and I am with him when he remembers Me. If he
remembers me to himself, I remember him to Myself; if he remembers Me in a
gathering, I remember him in a gathering better than it; if he draws near to
Me a handspan, I draw near to him an arm’s length; if he draws near to me an
arm’s length, I draw near to him a fathom’s length; if he comes to Me
walking, I go to him at speed.”

Narrated by al-Bukhaari, 7405; Muslim, 2675 

Ahmad (17020) narrated from Waathilah that the Prophet
(blessings and peace of Allah be upon him) said: “Allah, may He be glorified
and exalted, said: ‘I am as My slave thinks I am, so let him think of Me
however he wishes.’” Classed as saheeh by Shu ‘ayb al-Arna’oot in Tahqeeq
al-Musnad. So let her think positively of her Lord, may He be glorified,
and think that He will conceal her and suffice her, and accept her
repentance and put her affairs straight. 

She should understand that she has to conceal herself and not
tell anyone about her sin, neither her husband nor anyone else; rather she
should conceal that even if he asks her, and she should employ double
entendres. The hymen may be broken as a result of heavy menstruation,
jumping or other causes. 

If it so happens that someone knows what happened to her, he
should strive to conceal her first of all, then help her in her trial and
try to get hold of the video recorded by that evildoer by reminding him of
the punishment of Allah, may He be exalted, and the severity of the crime
that he has committed. If he is able to use threats with him and call upon
the authority of someone trustworthy who has any authority over him, in
order to scare him, that is good. 

We ask Allah to accept our repentance and that of the
believers, and to conceal our faults and protect us from worries and
anxiety. 

See also the answer to question no.
83093

And Allah knows best.