Does a girl's saying "Even if I enter Hellfire" while she is angry and not fully aware, take her out of Islam? And do her performing ablution and uttering the Two Testimonies after her regret restore her to it?

It appears that the speaker of this phrase intended to convey that she would not abandon charitable work regardless of her father's disapproval, and not that she insists on the sin of disobedience. Apostasy occurs only when one's heart is open to disbelief. Obedience to the father in this matter depends on whether there is a valid reason for his prohibition. If he has a valid reason, such as needing her or fearing for her safety, then obedience is obligatory. If he does not have a valid reason, then obedience is not obligatory, though it is preferable to obey him.

The guidelines for obeying parents are: the command must not involve disobedience [to God], they must have a valid reason for their command, and obedience must not result in harm to the child. If the parent's command arises merely from foolishness or lack of sense, it should not be heeded. However, the child should be cautious about disobeying the parent and exercise extreme care in such matters.