As you are on 75k, you are above the married standard rate cut off band.
Once she returns to work (assuming she will return in March 2020 after 4 months approx unpaid) she will be earning approximately 37k, allowing for 2 months unpaid plus a 20% deduction. She will still use all her tax credits on this salary so there is no real benefit in transferring any to you.
Your wife will be able to claim any tax overpaid in 2019 at the end of the year with her P21.
In 2020, when she returns to work she will have the benefit of the extra tax credits against her salary for a month or two.