Pet
Some of the ESA Descriptors refer to "significant discomfort", this is not defined but is considered to be less than significant pain, others make no specific reference to pain but it is still a factor that must be considered when assessed.
You don't say how your wife's limitations vary but if she is not able to complete an activity in a reasonable manner, for example; she is "great pain & discomfort" then it is for you to argue that she cannot do the activity, it will help if you have medical evidence to support the pain she is in and that it is reflected in the medication that she takes.
If you do tick "it varies" then you need to explain how the variation operates, for example; some claimants even at their best might struggle to complete an activity. In particular, you need to explain what she can do for the majority of the time.
Have a look at page 31 of the guide.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems