My partner regularly comes fishing with me; sometimes even for lengthy 3/4 day sessions. Fortunately, we live close to the venue (Sale Water Park), so she just nips home whenever she needs to freshen up! Until recently, she just came for the relaxation -- something that one gets accustomed to whilst targeting cats! -- although she is now proficient at catching livebaits for me whilst I set up the rest of my gear, which is a boon! She also takes excellent photographs, which is a god-send when most of the cat action occurs in the dark, early hours.
It is nice, from time to time, to enjoy some solitude, but if you have a patient, keen-to-learn partner, then I say go for it! When you're playing a lengthy waiting game, it's nice to have some company and someone you can burden with your fishing-related agonies as you await some action!
Damon.