She vowed to give all her wealth in charity but she owes zakaah. What should she do?

Firstly: 

Vows are not prescribed
in Islam because the Prophet (peace and blessings of Allaah be upon
him) forbade them. ‘Abd-Allaah ibn ‘Umar (may Allaah be pleased with him)
narrated: The Prophet (peace and blessings of Allaah be upon him)
forbade vows and said: “They do not ward off anything, but they are a means
of getting something out of the miser.” Agreed upon; this version was
narrated by al-Bukhaari. So every Muslim, man or woman, should keep away
from vows and not commit himself to something that he may be unable to do or
find it very difficult to do, thus falling into sin. 

Fataawa al-Lajnah al-Daa’imah,
23/362 

Although vows are basically makrooh, the person who vows to
do an act of worship is obliged to fulfil it, because the Prophet
(peace and blessings of Allaah be upon him) said: “Whoever vows to do an act
of worship, let him do it, and whoever vows to commit an act of sin let him
not do it.” Narrated by al-Bukhaari, 6202 

Secondly: 

Vowing to give some of one’s wealth in charity is a vow to do
an act of worship, so it is obligatory to fulfil it. 

If a woman vows to give all her jewellery in charity, one of
the following two scenarios must apply: 

1 – This jewellery is her entire wealth, in which case it is
sufficient for her to give one-third of it. This is the view of Ahmad (may
Allaah have mercy on him). 

Some of the scholars are of the view that it is obligatory
for her to give all her wealth in charity, such as al-Shaafa’i (may Allaah
have mercy on him). 

Ibn Qudaamah (may Allaah have mercy on him) said: 

Whoever vows to give all his wealth in charity, it is
sufficient for him to give one-third of it. This is the view of al-Zuhri and
Maalik… Abu Haneefah said: He should give all of his wealth that is subject
to zakaah…

Al-Shaafa’i said: He should give all his wealth in charity,
because the Prophet (peace and blessings of Allaah be upon him) said:
“Whoever vows to obey Allaah, let him obey Him.” And because it is a vow to
do an act of worship, so it is obligatory for him to fulfil it, like a vow
to offer prayers or observe fasts. 

The fact that it is sufficient to give one-third in charity
is indicated by the words of the Prophet (peace and blessings of Allaah
be upon him) in a hadeeth according to which Abu Lubaabah said:  “As a sign
of repentance I will give my wealth in charity for Allaah and His Messenger.
(The Prophet (peace and blessings of Allaah be upon him)) said:
“One-third is sufficient.” Classed as saheeh by al-Albaani in Takhreej
Ahaadeeth Mishkaat al-Masaabih, 3439. 

It was narrated that Ka’b ibn Maalik said: I said, “O
Messenger of Allaah, as a sign of my repentance, I will give up my wealth in
charity for Allaah and His Messenger.” The Messenger of Allaah (peace
and blessings of Allaah be upon him) said: “Keep part of your wealth for
yourself.” Agreed upon. According to a version narrated by Abu Dawood, “One
third is sufficient.” [Al-Albaani said in Saheeh Abi Dawood (3319):
its isnaad is saheeh.]  

End quote from al-Mughni, 11/340. 

i.e., if the wealth
specified in a vow refers to all of one’s wealth, the ruling is the same as
the ruling on one who vows to give all his wealth in charity; it is
sufficient for him to give one-third. 

Shaykh al-Islam Ibn Taymiyah said in al-Fataawa al-Kubra
(6/188): 

Concerning a person who vows to give all his wealth in
charity, the Sunnah is that it is sufficient for him to give one-third,
because giving all of it would cause hardship. End quote. 

Ibn al-Qayyim said something similar in I’laam
al-Muwaqqi’een, 3/165 

The correct view is that of the Hanafis, as stated in a fatwa
by the Standing Committee, when asked about one who vowed to give his entire
salary for the sake of Allaah on an ongoing basis. They replied: It is
sufficient for you to give one-third of your salary, because the Prophet
(peace and blessings of Allaah be upon him) said to one who vowed to
give all his wealth in charity: “One third is sufficient.” Narrated by Abu
Dawood. 

End quote from Fataawa al-Lajnah al-Daa’imah, 23/225 

2 – She has other wealth besides the jewellery, in which case
she must give all her jewellery in charity as she vowed to do. Ibn Qudaamah
(may Allaah have mercy on him) said: If a person vows to give a specific
thing or a specific amount of his wealth in charity, such as one thousand,
it is narrated from Ahmad that it is permissible to give one-third, because
it is wealth that he vowed to give in charity, so one-third is sufficient,
as is the case when giving all of one’s wealth. But the correct view
according to our madhhab is that all of it must be given in charity, because
it is a vow and an act of worship, so it must be fulfilled, as with all
other vows, because of the general meaning of the verse in which Allaah says
(interpretation of the meaning):   “They (are those who) fulfil (their)
vows…” [al-Insaan 76:7]. 

The reason why the fatwa is different with regard to one who
vow to give all of his wealth is because of the report narrated from the
Messenger of Allaah (peace and blessings of Allaah be upon him), and
because giving all of one’s wealth in charity could cause harm to a person.
al-Mughni, 11/340 

Thirdly: 

With regard to zakaah on
jewellery, she has to pay the zakaah for those eight years, regardless of
whether we say that she as to give all of her jewellery in charity or only
one-third of it – according to the discussion above – because zakaah is a
debt that she must pay, and it has nothing to do with the vow. But if she
has to give all the jewellery in charity, then she should pay the zakaah
from her other wealth, and she does not have to pay the zakaah from the
jewellery itself.

 If she has to give one-third of it in charity, then it is
permissible for her to pay the zakaah from the remaining jewellery, if that
is possible, or from her other wealth.