It seems she's got problems conceiving herself and they tried IVF from that article?
So using a surrogate for a child that's biologically yours is an alternative.
Having 4-5 pregnant with your child at the same time doesn't sit right with me (I'm guessing that looking at kids ages).
I can also understand wanting a large family and using alternative ways to achieve that if you can't conceive.
But not this way - a child every 18 months is more the right timescale.