As Salam O alikum,

after compliments.

I have a question with regards to Qadha Namaz for our marhoom walid. My question is that can we arrange a lady to offer the qadha namaz for our father, who is a sayyed widow and financially very troubled with a girl child to take care of? or only a man can offer the namaz for a man?
awaiting reply.

may Allah s.w.t bless you with good health.

Yes you can
May Allah grant exalted place in Jannah to your father