Her husband divorced her by talaaq and she married another man during the ‘iddah

Firstly: 

We
ask Allah to accept your repentance and set your affairs straight, and help
you to maintain your religious commitment. 

You
made a mistake by moving away from your husband and exposing yourself to
trials and tests, and your husband made a mistake by not allowing you to
work whilst not sending you any maintenance to spare you from having to
work. 

Secondly: 

If
your husband had divorced you twice, as you say, then your ‘iddah ended
before the second marriage, then you do not have to do anything and your
second marriage is valid in that case. 

The
‘iddah of a woman who menstruates is three menstrual cycles. If he divorced
you when you were in a state of purity (i.e., not menstruating) then you had
three menstrual periods, when you became pure following the third period and
did ghusl, your ‘iddah came to an end. 

The
‘iddah of a woman who does not menstruate because she is too young or has
passed menopause is three months. 

The
‘iddah of a woman who is pregnant ends when her pregnancy ends. 

If
the divorce was in return for payment from the woman, then this is khul‘, in
which case the ‘iddah is one menstrual cycle, according to the more correct
opinion. 

If
the second marriage contract was not done until after your ‘iddah ended,
then it is a valid marriage and you do not have to do anything, but it is
not permissible for you to go back to the first husband unless the second
husband divorces you and the ‘iddah following that divorce comes to an end.
Then the first husband can do a marriage contract with you. 

But
if your second marriage was done during the ‘iddah, then it is an invalid
marriage and does not count, and you have committed a grave and serious evil
by doing that. 

Ibn
Qudaamah said: With regard to invalid marriages, such as marriage to a woman
who is married or still in the ‘iddah period, and the like, if they were
aware of what is halaal and haraam in this regard then they have committed
zina and are subject to the hadd punishment, and any child born as a result
cannot be attributed to the man. 

End
quote from al-Mughni, 7/10 

And
he said: If he marries a woman who is still in the ‘iddah period and they
both knew about the ‘iddah and that marriage is forbidden during that
period, and he had intercourse with her, then they have committed zina and
are subject to the hadd punishment for zina, she is not entitled to any
mahr, and any child born as a result cannot be attributed to the man. 

If
they were both unaware of the ‘iddah and the prohibition (on marriage at
that time), then any child born as a result is to be attributed to the man
and no hadd punishment is to be carried out, and she is entitled to the
mahr. 

If he
was aware of that but she was not, then he is subject to the hadd punishment
and must pay the mahr, and any child born as a result is not to be
attributed to him. 

If
she was aware of that but he was not, then she is subject to the hadd
punishment and is not entitled to any mahr (dowry), and any child born as a
result is to be attributed to the man. 

That
is the case because this is a marriage concerning which there is consensus
that it is invalid; it is akin to incest.  

End
quote from al-Mughni, 8/103 

In
that case the second marriage is annulled because it is invalid, and you
have to complete the ‘iddah from the first marriage, then observe ‘iddah
from the second marriage. Then can you go back to your first husband or
not? 

–
If he had taken you back
during the ‘iddah – even if that was without your knowledge – or he took you
back during the completion of the ‘iddah for his divorce, then you are still
his wife.

–
If the ‘iddah ended without
him taking you back, then he is a stranger (non-mahram) to you and you
cannot go back to him except with a new marriage contract. In that case you
have the choice between marrying him or the second one or someone else.

The
point is that marrying another man during the ‘iddah is invalid, whether the
first one took you back during the ‘iddah or not, and whether you will go
back to him with a new marriage contract or not. 

And Allah knows best.