Hi,
Presumably your wife's DLA medical is in your own home as the majority of DLA medicals are. if not you can ask for the examination to take place in your home, if your wife is unfit to attend a medical centre.
Whilst the Medical Examiner will usually put any questions to your wife, as her husband and it appears that you're her carer also, there is nothing to stop you from contributing and explaining to the EMP the extent of your wife's care and mobility needs, especially if her medication makes it difficult for her to explain things herself.
The medical for DLA purposes is not like for example a medical your GP would carry out to make a diagnosis. With DLA the name of the claimant's condition is secondary. What is paramount is the severity of your wife's mobility and/or care needs, so the EMP's examination will be to determine if your wife's needs have changed, i.e. improved or worsened. It's not the EMP who makes the decision on an award of DLA, it's done by a Decision Maker (DM) from the DWP. After the medical is complete, the EMP sends it to the DWP's DM who makes the decision.
If you wish, once the DWP receive the EMP report you are legally entitled to a copy under the Data Protection Act 1998.
The guidance given to EMP's is that they should not make decisions about a claimant's needs based on a 'snapshot' on a particular day, but should take all things into consideration. 'Guidance for EMP's' is in the members area as are the '70 Questions You’re Likely To Be Asked At Your DLA Medical'
HERE
Hope this adds to what Gareth has advised.
Jim