She made several vows but then forgot them

Whoever makes a vow to do an act of worship such as praying,
fasting, giving charity etc must fulfil that vow, because the Prophet
(peace and blessings of Allaah be upon him) said: “Whoever vows to obey
Allaah, let him do so, and whoever vows to disobey Allaah, let him not do
so.” Narrated by al-Bukhaari, 6318. This applies whether the vow was
connected to something happening or was made in general terms. 

Ibn Qudaamah (may Allaah have mercy on him) said concerning a
vow to do an act of worship: 

These vows are of three
types, one of which is obliging oneself to do an act of worship in return
for a blessing which one hopes to have or a harmful thing which one seeks to
ward off, such as when a person says, “If Allaah heals me then I will fast
one month for Allaah.” In this case the act of worship is something which is
basically obligatory according to sharee’ah, such as prayer, fasting,
charity and Hajj. This vow must be fulfilled according to scholarly
consensus. 

Al-Mughni, 13/622. 

If you can remember what you vowed to do – such as praying,
fasting or giving charity – but you do not know how much you said you would
do, then you have to try your best, and do whatever you think is most
likely, so that you will have fulfilled your obligations. 

But if you have forgotten or are uncertain as to whether what
you vowed to do was praying or fasting or giving charity, then in this case
some of the scholars are of the view that you must do your best to do one of
them, and some are of the view that what you must do is to offer kafaarat
yameen, for each vow of which you are uncertain. Mughni al-Muhtaaj,
6/234; Ghamz ‘Uyoon al-Basaa’ir, 1/211; al-Mawsoo’ah al-Fiqhiyyah,
26/201. 

Hence you will know the
answer to your second question. A vow to offer a prayer must be fulfilled,
so you must do whatever you think is most likely to discharge your
obligation. If you are uncertain as to whether you vowed to do twenty
prayers or twenty-five, then do twenty-five. 

It should be noted that we should not make vows, because of
the report narrated by al-Bukhaari (6608) and Muslim (1639) from Ibn ‘Umar
(may Allaah be pleased with him) who said: The Prophet (peace and
blessings of Allaah be upon him) disallowed making vows and said: “They do
not change anything, all they do is make a miser give [in charity].” 

And al-Bukhaari (6609) narrated from Abu Hurayrah that the
Prophet (peace and blessings of Allaah be upon him) said: “Allaah says:
‘A vow does not bring the son of Adam anything that I have not decreed for
him, but his vow may coincide with what has been decreed for him, and in
this way I cause a miser to spend of his wealth.’” 

And Allaah knows best.