Its not that bad. I think the two most important consideration are 1) does it add anything new that an adcomm would look favorably on that wont be in my other two recs? and 2) are the other two recs likely to be MUCH better?
If yes to 1 and no to 2 then you should send it.
If yes to both its a tossup IMO
If no to 1 and yes to 2 then you should make it inactive
If no to both its a tossup IMO
Sorry for writing that in such a weird way but thats the way I view it. I think it would help your situation a lot if you have read your other two LORs...it would help you evaluate what to do much better.
1. Yes, slightly. It probably adds a little that the other recs might not have mentioned.
2. Yes, probably. One of the other LORs is written by a writing teacher (in the business writing program). She is an "English-y" person and is a very good writer obviously. She knows exactly what to do I'm sure. She knows how to "show, not tell".
The other one is by a former lawyer. She is very intelligent and is a great writer. She writes in a really logical way too. And also, she really liked my writing.
Might I add that both of these women were on sabbatical this semester, so they obviously had plenty of time to write my LOR (unlike the LOR that I posted above, which was obviously somewhat rushed).
So I guess it's kind of a tossup, leaning more towards the side of dumping the mediocre LOR.