Mike, I think I may be a helpful person to give my opinion on this. I have seen Fish In The Dark. I sat in row A orchestra center on the aisle. That is the third row of the center section. I am going back to see the show again this coming weekend, and I purchased orchestra left, row BB seat 1 on the aisle, one of the exact seats you are considering. I also like to sit close whenever possible, so I understand your friend's needs.
The stage is moderately high. It is not very high, and it is not low. When I saw the show the first time, I took a good look at the first two rows - rows AA and BB of the center section, and the front row of the side sections - row BB, thinking that I wanted to return to see the play again with Jason Alexander. I decided that center row AA was just a little too close because of the stage height, but that row BB was ok. Also, since row BB is the front row on the sides, it is nice that nobody is in front of you. And in my opinion, seeing this play from the side instead of the center is not a big problem.
Given your friend's needs, my suggestion is most definitely the aisle seat on either orchestra side section, rather than the mez. I know that many people enjoy the view from the mez, but I don't think it sounds like your friend fits in that category. And I have seen the stage height up close, and in my opinion row BB is just fine, so much so that I am sitting there myself later this week. I hope that helps.