Thanks for your question, I am Sam and I am one of the UK tax experts here on Just Answer.
If the proeprty is owned jointly, hen the rental income must be split 50:50 unless its a fact that your wife contributed a higher share than 50% to its purchase. If not, then I am afraid no election to aleter the 50:50 position would be accepted by HMRC.
The other consideration would be to transfer the property into your wifes sole name so that she is the sole owner, and in this instance then she can be treated as receiving 100% of the rental income.
Let me know if you need any further advsie on this matter or have any questions