She has a strong desire to have a baby and is praying for that, but her husband wants to delay having a baby, and now she is frustrated

One of the aims of marriage in Islam is to produce offspring and increase
the numbers of the ummah. Abu Dawood (2050) narrated that Ma‘qil ibn
Yasaar (may Allah be pleased with him) said: The Messenger of Allah
(blessings and peace of Allah be upon him) said: “Marry those who are
loving and fertile, for I will be proud of your great numbers before the
nations.” Classed as saheeh by al-Albaani in Saheeh Abi Dawood
(1805). 

Having children is the right of both spouses, and neither of them can regard
that as his or her own right to the exclusion of the other. If the wife
wants to have children, the husband does not have the right to prevent her
from doing so. Hence the fuqaha’ stated that the husband should not engage
in ‘azl (coitus interruptus – withdrawing before ejaculation) with his wife
except with her permission. 

Delaying pregnancy for fear of not being able to afford to spend on the
children’s maintenance implies that one thinks negatively of Allah, may He
be exalted, because Allah, may He be glorified and exalted, has guaranteed
to provide for them, as He says (interpretation of the meaning):
“We
provide for them and for you”
[al-Isra’ 17:31]. Having
a lot of children is also encouraged by Islamic teaching. The believer
should think positively of his Lord, may He be exalted, and remember that He
is the provider. If people were to pay attention to such fears, they would
have few offspring, which would result in the opposite of what the Lawgiver
seeks, which is to increase their numbers. 

Based on that, you do not have to obey your husband and use contraceptives,
because of what that results in of the loss of your rights. You may also use
tricks to enable you to have children, which is one of the important aims of
marriage. But we advise you to work out this issue between you, and explain
it to him and tell him that provision is in the hand of Allah. Who knows?
Perhaps this child would be a cause of opening the gates of provision to
you. Moreover, family planning for most people does not start with the first
child! What is it that made him get married in the first place? What is
expected is to have one or two children, then to pause for a while, whatever
is appropriate to the mother’s condition or the family’s situation. But to
start with the first child and say that he will not have children until
after some time, this is very strange. 

If
it so happens that the matter is delayed for some time, even for a number of
months, and you cannot convince your husband, then be patient. Perhaps Allah
will guide him and will fulfil your need. But do not stop offering
supplication, because it is one of the noblest acts of worship and one of
the greatest means of attaining what you seek, and think positively of your
Lord, may He be glorified and exalted, in all things. 

And Allah knows best.