I do know that there have definitely been a few blind MPs before (I have a list somewhere but I can't find it) but David Blunkett is the first one to use a guide dog. DB has been an MP since 1987, so I think he probably had at least one guide dog before Lucy - they only have a working life of about 8 to 10 years, so Lucy must have started after 1987 because she retired only a year or two ago.
It is, of course, possible that there may be a completely different answer other than guide dogs. How about rescue dogs after the House of Commons was bombed in WW2?