secondary infertility

It's easy to say 'be thankful for the child you have' but so many people are unable to conceive at all.

I think most only children are a result of secondary infertility.
DD1 has only one child and I went to school with plenty of them.
Telling your DDs not to worry doesn't help, can't help.
You just have to accept it.
Pressure from Mum is awful- Pull yourself together and keep quiet about it. Don't go into long discussions about it.

It sounds as if stress and anxiety could be a factor in her inability to conceive.
It is so easy to say - relax, don't think about it and it will happen but perhaps they can both take positive steps to enjoy their family life, stop 'trying' and, as there is no physical cause, conception could happen when they are least thinking about it.

IVF can be quite a traumatic experience and could have side effects for a woman.

You have a lot of worries at the moment and I realise your DD is very stressed and you want to support her but you must not allow this to dominate all your lives. Sorry if that sounds harsh but your mother and your DH need your love and care too. Your other DD should not feel guilty either about trying for another baby.

I have, elder daughter had one child but still no second five years on, younger daughter no baby. Both were prescribed medication , can't recall name, elder daughter pregnant, younger no. Elder distressed over younger but she needed to accept she being pregnant and younger not being we're not related . Younger daughter had , I think sixteen attempts of IVF over twenty years , this year it failed again and she has finally accepted she will not have a child. Elder had a third child less than two years after second .i was also carer for both my parents at the time.

So I do understand how you feel. But I think your daughter who is reluctant to have a child because her sister may be upset should be encouraged to have the child she wants,