How can I allow 2 users on my iPad?

An iPad is a single-user device. 

Unlike other computers with which you may be familiar, that support multiple user profiles - other than “managed” educational environments, OS/iPadOS devices are not intended to be shared.

Be aware that if you sign-out of iCloud and other Apple services - and allow another user to sign-in - you’ll not be able to change back for 90-days.

So as to prevent account abuse, some critical Apple services will only allow one change of signed-in AppleID (on a device) in a 90-day period.

In conclusion, unless you fully understand and accept the implications, you would be well advised to reconsider any attempt to share your iPad with another user.

iPads can only be used by a single user. The best solution would be to get a new iPad for your wife.