She will be going to hell.
Allah says in the Qur'an, chapter 3 verses 18-19:
"Allah witnesses that there is no deity except Him, and [so do] the angels and those of knowledge - [that He is] maintaining [creation] in justice. There is no deity except Him, the Exalted in Might, the Wise. Indeed, the religion in the sight of Allah is Islam. And those who were given the Scripture did not differ except after knowledge had come to them - out of jealous animosity between themselves. And whoever disbelieves in the verses of Allah, then indeed, Allah is swift in [taking] account."
Allah also says in the Qur’an chapter 2 verse 217:
“...while whoever of you turns away from his faith and dies an infidel,
such people are those whose deeds will go to waste in this world and
in the Hereafter, and they are people of the Fire. They shall be there forever.”
Allah also says in the Qur'an chapter 2 verse 6:
“Indeed, those who disbelieve - it is all the same for them whether you warn them or do not warn them - they will not believe.”
Allah also says in the Qur'an chapter 4 verses 136-137:
"O you who have believed, believe in Allah and His Messenger and the Book that He sent down upon His Messenger and the Scripture which He sent down before. And whoever disbelieves in Allah, His angels, His books, His messengers, and the Last Day has certainly gone far astray. Indeed, those who have believed then disbelieved, then believed, then disbelieved, and then increased in disbelief - never will Allah forgive them, nor will He guide them to a way."
Allah says in the Qur'an chapter 2 verse 90:
"How wretched is that for which they sold themselves - that they would disbelieve in what Allah has revealed through [their] outrage that Allah would send down His favor upon whom He wills from among His servants. So they returned having [earned] wrath upon wrath. And for the disbelievers is a humiliating punishment."
I think you get the idea now.
You might argue that Qur'an 2:62 means that Christians and Jews will also go to heaven because they believe in God and the last day and (some) do good. However, Allah says in the Qur'an chapter 3 verse 85:
"And whoever desires other than Islam as religion - never will it be
accepted from him, and he, in the Hereafter, will be among the losers."
Originally, the verse refers to the Christians and Jews before Islam. As long as they followed their prophet accordingly, their deeds would not be cancelled out.
So, to conclude, because your friend was formerly Muslim but later converted to Christianity, she will not be going to heaven at all, but rather in hell if she does not return back to Islam.
"Indeed, they who disbelieved among the People of the Scripture and
the polytheists will be in the fire of Hell, abiding eternally
therein. Those are the worst of creatures."