Hi
There are a number of alternatives to your problem..
However each have there own problems and expense.
Firstly the recording source, you can buy a plethora of alternatives nowadays, but the easiest solution would be to buy a DAB radio with a USB recording facility, so you can record in digital format ( a lot use SD cards, which is affectively the same, but using SD cards on other devices is still limited ) so you have now a portable device ( think of it as a cassette with better sound quality and huge storage, even a basic 1GB uSB drive if recorded at 192kb will be the equivalent of 10 - 12 C90 cassettes, and if it is spoken word you will only need to record at 128kb which will give you about 20 or more C90`s )
The next step is again quite forward, dependant on how much you want to spend really.
The best long term solution is to go to somewhere like halfords ( who sometimes fit free ) and ask for the cheapest CD / USB head unit to replace your wifes existing one ( i dont know your budget or what type of car she has, just surmising that it will be pre 2003 as most manufacturers stopped putting tape players by then ) This should be a huge improvement on the sound quality compared to your existing tape player. Plus she will be able to skip ahead with ease rather than guessing if need be.
Other alternatives are using a modern smartphone as an mp3 player, you will need to buy a cassette adaptor sold for less than £2 nowadays
http://www.ebay.co.uk/itm/CAR-CASSETTE-ADAPTER-MP3-TAPE-PLAYER-IPHONE-IPOD-MP3-CD-RADIO-STEREO-NANO-3-5mm-/310635947026?pt=UK_AudioVideoElectronics_PortableAudio_MP3PlayerCarKits&hash=item4853586412
You can also use that with portable mp3 devices etc, there are a lot more alternatives out there, but if it is something your wife enjoys on a regular basis, I would opt for my original suggestion.
Best wishes